-7
Step-by-step explanation:
3x + 2 + 12 = 4x -2 + 9
3x + 14 = 4x + 7
-4x  -14   -4x  -14
-1x = 7
x= -7
coin flip
non-answer:
choosing
sorry if this isnt what you're looking for i dont really understand the question
i think it would be 42cm