Let me explain the train of thought, and write the rest yourself.

The most important thing about this problem is the congruence of triangles. I don't know if you have learned it. After drawing, I found the triangle DAE and DAB congruence (SAS).

So the angle DAE= angle b, and because of the proportional relationship, angle BAC+ angle B=90 degrees =5 angle b, so angle B= 18 degrees.