Answer:
Step-by-step explanation:
Your problem setup is correct. The triangle is isosceles, so the marked segments are the same length.
3x - 8 = 2x
You can solve this by subtracting 2x (from both sides) ...
x - 8 = 0
Then adding 8 (to both sides):
x = 8
MB = MA = 2x = 16.