Question

What is the equation

Answer 1

Look at the picture.

The slope-point formula:

$y-y_1=m(x-x_1)\\\\m=\dfrac{y_2-y_1}{x_2-x_1}$

We have the points (30, 120) and (40, 100).

Substitute:

$m=\dfrac{100-120}{40-30}=\dfrac{-20}{10}=-2\\\\y-120=-2(x-30)\\\\y-120=(-2)(x)+(-2)(-30)\\\\y-120=-2x+60\qquad|+120\\\\\boxed{y=-2x+180}$