3x+2y=4
y=-2x+3
Ugg, what the heck is subsitution.. hmm sounds familar, perhaps:
3x+2y=4
y=-2x+3
First solve for x, or y, it doesn't matter, I am solving for x.
3x = 4-2y
x = 4/3 - 2y/3
Now subsitute x for the value I above, and solve for y. Then use the y answer (which should be one number, not an expression) to solve for x.