Answer:

Explanation:
The asterisk means degree sign in the following solution.
The measure of the smaller angle in the triangle is 180* - 153*.
The measure of b is 180* - (180* - 153*) - 90* (because the sum of angles in a triangle is 180*).
b = 180* - (180* - 153*) - 90* = 153* - 90* = 63*