You are given two points on the line: (-2, 15) and (1, 0). (the x-int is where y equals zero)
This allows you to use the slope formula to solve the slope, m. (see first image, first equation in red). The slope is 15.
Then, as in the second picture, plug in the slope and a point into the point slope equation. I used the point (1, 0) but using the other point should yield the same answer.
To change it to slope intercept form, distribute the slope to the numbers in the parentheses and then add/subtract the number on the left side to have y by itself. The answer ended up as y=15x-15