Answer:
x=9
Step-by-step explanation:
1. If you're given the possible solutions then just substitute x for the possible solutions given.
3(5) - 6 = 9, so A is incorrect.
3(1) - 6 = -3, so B is incorrect.
3(12) - 6 = 36, so C is incorrect.
3(9) - 6 = 21, so D is correct.
