Question

If triangle ABC is congruent to triangle DEC, angle B = x + 15 and angle E = 6x - 65

Answer 1

If triangle ABC is congruent to triangle DEC, then all the lengths and angles in the one triangle are equal to their corresponding lengths and angles in the other triangle.

In other words, Angle B = Angle E

x+15 = 6x-65

Now solve for x:
-80 = 5x
-16 = x