This is an isosceles triangle because the 2 base angles are equal and therefore the 2 sides MN and ML are equal also.
So 3x = x + 10
2x = 10
x = 5
Length of MN = 5 + 10 = 15 Answer
This is the picture of the triangles.
triangle ABC. is rotated 180 degrees about point (0,0)
good luck
I hope this is what you were looking for! x^2 + xn + xm + mn