4x−3y=12
7x−3y=3 Important: you have two -3y terms. Mult one eqn by -1 to
obtain +3y, and then add the 2 equations together:
4x - 3y = 12
-7x+3y = -3
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-3x = 9, so x = -3. Subst. -3 for x in the first original equation to find y:
4(-3) - 3y = 12, or -3y = 24. Then y = -8.
Solution is (-3, -8).
It's important that you check this answer by subst. (-3, -8) back into either one of the original equations.