I could please use some help.

Answer:
30
Step-by-step explanation:
Congruent triangles have congruent corresponding sides and angles. If triangles ABC and DEC are congruent, then
Consider triangle DEC. In this triangle,
The sum of the measures of all interior angles in triangle are always 180°, so
[tex]m\angle C+m\angle D+m\angle E=180^{\circ}\\ \\55^{\circ}+65^{\circ}+m\angle E=180^{\circ}\\ \\m\angle E=180^{\circ}-55^{\circ}-65^{\circ}\\ \\m\angle E=60^{\circ}[/tex]
Hence,
[tex]m\angle B=60^{\circ}[/tex]
So,
[tex]2x=60\\ \\x=30[/tex]