Question

Abc = dfe find the value of x.

Answer 1

BC ≅ EF (CPCTC)

Set the two side lengths equal to each other.

38.4 = 5x - 10.6

Isolate the x. Add 10.6 to both sides

38.4 (+10.6) = 5x - 10.6 (+10.6)

5x = 49

Isolate the x, divide 5 from both sides

5x/5 = 49/5

x = 49/5

x = 9.8

9.8 should be your answer

hope this helps

Answer 2

I think you're telling us that the two triangles are congruent ...
all the sides and angles of one triangle are equal to the sides
and angles of the other one.

OK.  That means that (5x - 10.6) = 38.4

Add 10.6 to each side:  5x = 49

Divide each side by 5 :  x = 49/5 or 9.8