Answer:
18
Step-by-step explanation:
If two triangles are congruent, their angle measures are the same.
Depending on the placement of the letter, you are able to identify which angles correlates. A correlates with D, B with E and C with C. In this case, we are given angle B and we are solving for E. We know B=E so we set up an equation
2x+4=40
Subtract 4 to both sides
2x=36
x=18
