Question 240059
A = P+PRT --------- solve for P 
Factor the right side:
A = P(1 + RT)
Solve for "P":
P = A/(1 + RT)
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A = (1/2) h (B+b) ------------- solve for b
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Multiply both sides by 2 to get:
2A = h(B + b)
Divide both sides by "h":
B + b = (2A)/h
Subtract "b" from both sides.
b = [(2A)/h] - B
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Cheers,
Stan H.