Answer:
12
Step-by-step explanation:
Since the base angles are congruent, this means this is an isosceles triangle. This means that the sides adjacent to the base angles are congruent.
This gives us the equation
3x=x+8
Subtract x from each side:
3x-x = x+8-x
2x = 8
Divide both sides by 2:
2x/2 = 8/2
x = 4
Plug this into MN:
4+8 = 12
