A=1/2h (b1 + b2)

Solve for b1

A=1/2h (b1 + b2)

Solve for b1

I assume this is A = (1/2)(h)(b1 + b2); i.e., the h is in the numerator and not the denominator
Multiply both sides by 2.
2A = (2*1/2)h(b1 + b2).
2*1/2 on the right side is 1.
2A = h(b1 + b2)

expand the right side.
2A = hb1 + hb2.

Subtract hb2 from both sides.
2A - hb2 = hb1 + hb2 - hb2.
The hb2 terms on the right "cancel" or add out.
2A - hb2 = hb1

Divide both sides by h, leaving just b1 on the right side.
[(2A - hb2)/h] = (hb1/h) = b1

I hope this helps. Check my work.

If I divide everything by 2 at the end. Where does the A go.

Would it be Ab2/h = b1

Im kind of lost

Why do you wish to divide everything by 2 from the last step? That will give you 1/2*b1 on the right and you wanted to solve for b1, not 1/2 b1.
Just remember that you can do anything to the equation to get it in the form you wish but whatever you do to one side you must do to the other side. If you are still lost, post what step you don't understand and tell us exactly the problem you are having in taking the next step.

thank you for the help.

is the equation if you were solving for B2
[(2A-hb2)/h]=(hb2/h)=b2 ?????

So what's the answr in the end??

what if i was solving for h? what would i do?

A=1/2h(b1+b2) Solve for h

To solve for b1, the final equation is:

b1 = (2A - hb2) / h

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