An increasing (or decreasing?) line

We're told that if $x$ decreases by 2, then $y$ decreases by 4. In terms of slope, this means $m = \frac{\Delta y}{\Delta x} = \frac{-4}{-2} = 2$ .

We're also told that the line passes through $(2, 90)$ , so we can use point-slope form to find the equation of the line:

$y - 90 = 2(x - 2) \longrightarrow y = 2x + 86$

The $y$ -intercept is 86 and the $x$ -intercept is -43, the sum of which is 43.