Answer: Upper right corner (northeast corner)
x-3y = 15
===================================================
Explanation:
The y intercept <u>always</u> occurs when x = 0.
If we plug x = 0 into 2x+y = -10 (northwest corner), then we solve for y to get...
2x+y = -10
2(0)+y = -10
0+y = -10
y = -10
We see that the y intercept here is -10, but we want -5 instead. So we can rule this out.
In the northeast corner, plugging x = 0 leads to,
x-3y = 15
0-3y = 15
-3y = 15
y = 15/(-3)
y = -5
We get the correct y intercept we're after. So we can stop here.
If you plugged x = 0 into the equation of the southwest corner, you'll get y = 5 which is fairly close but not quite what we want. The southeast corner equation leads to a y intercept of y = 5 as well.
