Answer :

mumsy
In order to find b1 from your formula stated we need to do few calculations
A=hb1+hb2, as you wee I multiply h with both bases( b1 and b2)
I will subtract hb2 from both sides
hb1=A-hb2
now I will divide my new expression by h
b1=(A-hb2)/h
solve like a regular algebraic expression A= h(b1+b2) divide both sides by h A/h= b1+b2 subtract b2 from both sides A/h-b2= b1 b1= A/h-b2 hope this helps