We should simplify to y=mx + b first:
3x=4y+12
-4y=-3x+12
(/-4)
y=3/4x-3
To solve for the y intercept we set x to 0 and solve:
y=3/4(0)-3
y=-3
To solve for the x intercept we do the opposite and set y to 0 and solve:
(0)=3/4x-3
(*4)
0=3x-12
-3x=-12
(/-3)
x=4