Here are two examples of simplifying rational expressions where the denominators are already the same.

Let's solve each of the given problems step by step.

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Problem 7:

$$
\frac{4y}{y-3} - \frac{5y}{y-3} + \frac{2y}{y-3}
$$

Step 1: All terms have the same denominator, $ y - 3 $, so we can combine the numerators directly:

$$
\frac{4y - 5y + 2y}{y - 3}
$$

Step 2: Simplify the numerator:

$$
4y - 5y + 2y = (4 - 5 + 2)y = 1y = y
$$

So the expression becomes:

$$
\frac{y}{y - 3}
$$

✔ Answer for Problem 7:
$$
\boxed{\frac{y}{y - 3}}
$$

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Problem 9:

$$
\frac{6xy^2}{4a + 12} + \frac{3xy^2}{4a + 12} - \frac{xy^2}{4a + 12}
$$

Step 1: All terms have the same denominator, $ 4a + 12 $. So combine the numerators:

$$
\frac{6xy^2 + 3xy^2 - xy^2}{4a + 12}
$$

Step 2: Simplify the numerator:

$$
6xy^2 + 3xy^2 - xy^2 = (6 + 3 - 1)xy^2 = 8xy^2
$$

So the expression becomes:

$$
\frac{8xy^2}{4a + 12}
$$

Step 3: Simplify the denominator:

Factor $ 4a + 12 $:
$$
4a + 12 = 4(a + 3)
$$

So:
$$
\frac{8xy^2}{4(a + 3)} = \frac{8}{4} \cdot \frac{xy^2}{a + 3} = 2 \cdot \frac{xy^2}{a + 3}
$$

✔ Answer for Problem 9:
$$
\boxed{\frac{2xy^2}{a + 3}}
$$

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✔ Final Answers:

- Problem 7: $ \boxed{\frac{y}{y - 3}} $
- Problem 9: $ \boxed{\frac{2xy^2}{a + 3}} $

Let me know if you'd like these explained in more detail!