Area of a trapezoid

Question

solve for b1: A= 1/2h(b1= b2)

Answer 1

Looks like a typo
A = (1/2) h (B1+B2)

2 A = h B1 + h B2

h B1 = 2 A - h B2

B1 = (2 A - h B2) / h

Answer 2

Next time try to write it in the correct format ok ty :)