Write a linear equation that describes earnings.

I've been stuck on this question for ages because my teacher never taught it to us. I would greatly appreciate if someone explained it :)

Determine the graph that correctly represents the reflection. When Kristin works 8 hours, she earns $60. When she works 20 hours, she earns $150. Write a linear equation that describes her earnings. Assume that the changes increase linearly.

The graph of this equation has hours as the x axis and earnings as the y axis.

The line passes through two points (8,60) and (20,150).

The two-point form of a linear equation is

(y1 - y)/(x1 - x) = (y2 - y1)/(x2 - x1)

In this case
x1 = 8
y1 = 60
x2 = 20
y2 = 150

so
(60 - y)/(8 - x) = (150 - 60)/(20 - 8) = 7.5
60 - y = 7.5(8 - x)
60 - y = 60 - 7.5x
y = 7.5x

or
earnings = 7.5 * hours

or
Kristin's hourly rate is $7.50