Answer:
8x -7y = 56
Explanation:
You want an equation for a line that has x-intercept 7 and y-intercept -8.
Intercept form
The intercept form of the equation of a line with x-intercept 'a' and y-intercept 'b' is ...
x/a +y/b = 1
For the given intercepts, this equation becomes ...
x/7 +y/(-8) = 1
Multiplying by 56 puts this equation in standard form.
8x -7y = 56