First angle orthographic projection showing a 3D stepped block with dimensions and view orientations.

This image presents a task related to "First angle orthographic projection," which is a standard method in technical drawing for representing a 3D object in 2D. The goal is to create the 2D views (Plan, Front Elevation, and End Elevation) of the 3D object shown.

Let's break down the solution step by step.

Step 1: Understand the 3D Object

The 3D object is an L-shaped block composed of three rectangular prisms stacked together.
- Dimensions: The overall dimensions are given as 50mm (width), 40mm (depth), and 90mm (height, made up of three 30mm sections).
- Color Coding: The object is colored to help distinguish its parts:
- Yellow: The main base and back section.
- Red: A middle section on the left.
- Blue: A top section on the left.

Step 2: Define the Views

In first-angle projection, the views are arranged as follows:
- Plan (Top View): Placed above the front view.
- Front Elevation (Front View): The primary view, placed in the center.
- End Elevation (Side View): Placed to the right of the front view.

The arrows indicate the direction from which each view is projected.

Step 3: Draw the Plan (Top View)

Looking down from the top:
- You see the top surfaces of all three sections.
- The overall shape is a rectangle 50mm wide and 40mm deep.
- Inside this rectangle, you will see lines indicating the edges of the different levels.
- A vertical line at 20mm from the left edge separates the yellow and red/blue sections.
- A horizontal line at 30mm from the front edge separates the yellow base from the red/blue sections.

Step 4: Draw the Front Elevation (Front View)

Looking from the front:
- You see the front faces of the object.
- The overall height is 90mm and the width is 50mm.
- The object has a stepped appearance:
- From the bottom to 30mm height: a full 50mm wide section (yellow).
- From 30mm to 60mm height: a 20mm wide section on the left (red).
- From 60mm to 90mm height: a 20mm wide section on the left (blue).

Step 5: Draw the End Elevation (Side View)

Looking from the right side:
- You see the side faces of the object.
- The overall height is 90mm and the depth is 40mm.
- The object appears as a single rectangle because the red and blue sections are aligned with the yellow section in depth.
- However, there will be hidden lines or a change in shading to indicate the different levels if required, but typically, only visible edges are drawn.

Final Answer

To solve the problem, you need to draw the following 2D views based on the 3D object:

1. Plan (Top View):
- A 50mm x 40mm rectangle.
- A vertical line at 20mm from the left.
- A horizontal line at 30mm from the front.

2. Front Elevation (Front View):
- A 50mm wide by 90mm high shape with steps:
- Bottom 30mm: 50mm wide.
- Middle 30mm: 20mm wide on the left.
- Top 30mm: 20mm wide on the left.

3. End Elevation (Side View):
- A 40mm deep by 90mm high rectangle, showing the full height and depth without any internal lines since all sections align in depth.

These views together provide a complete representation of the 3D object in 2D, following the rules of first-angle orthographic projection.