Graph of cost over time for two linear equations, highlighting y = x + 4 with a slope of 1 and y-intercept at (0, 4).

A graph showing two linear equations, y = x + 4 and y = 2x + 1, with the first equation plotted using a blue line. The x-axis represents minutes and the y-axis represents cost in dollars. The line for y = x + 4 passes through the point (0, 4) with a slope of 1, illustrated by moving up 1 and right 1 from the y-intercept.