Question

Which ordered pair is the solution to the system of equations? x+y=-1

3x-y=21
A. (5, -6)
B. (7, -8)
C. (5.5, -6.5)
D. (10, -11)

Answer 1

You use substitution and trial and error to answer this, so for A, every time you see an X you'd replace it with 5, and every time you see a Y you'd replace it with -6. Luckily, the answer is a because after substitution, the sum is correct:
5 + (-6) = -1
(3 × 5) - (-6) = 21