10. solve the system of equations 3y + 2z = 12 and y – z = 9. a. y = 6, z = –3 b. y = 24, z = 15 c. y = 6, z = 15 d. y = –6, z = 15

3y + 2z = 12
Now you just try every answer until you get the right one.
A) y=6 z=-3
3×6 + 2×(-3) =18 -6=12
This is CORRECT
B) y=24 z=15
3×24 + 2×15= 72 + 30 =102
This is INCORRECT
C) y=6 z=15
3×6 + 2×15=18+30=48
This is INCORRECT
D)y=-6 z=15
3×(-6) + 2×15 = -18 + 30 = 12
This is CORRECT
So the correct answers are A and D