[tex]A=\frac{1}{2}h(B+b)[/tex] Solve for b (isolate/get b by itself):
[tex]A=\frac{1}{2}h(B+b)[/tex] Multiply 2 on both sides to get rid of the 1/2
[tex]2A=h(B+b)[/tex] Divide h on both sides
[tex]\frac{2A}{h} =B+b[/tex] Subtract B on both sides
[tex]\frac{2A}{h}-B=b[/tex]
