Step-by-step explanation:
The sum of inner angles of a triangle is 180°, or another way of saying is, the angles of the there's corners of the triangles, if u add them all, it will always be 180°, therefore
90 +71 + b = 180
b = 19
Ok now since it is a straight line,
B + a = 180
19 + a =180
a = 161
