I thought I knew this stuff but now I'm starting to wonder. I've tried several times but I haven't been able to figure this out. there is also a diagram showing a water line where the y intercept is crossing over (0,-12).

the question is

Q: what is the slope and the y intercept of y = - 2/3x - 12

A: slope equals: - 2/3

the y intercept is: (0,-12)
Q: how do you know this is the y intercept?
A: I don't know. this is what I got but it doesn't make sense....

because if I replace y with 3 then
x = - 10 (3,10)
if i replace x with 3 then y = -14 (3,-14) when placed on a grid they cross over y intercept at -12

what am i doing wrong?!!!