FV-O/T=A for o

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FV-O/T=A for o

Add O/T to each side:
FV-O/T + O/T = A + O/T

We have:
A + O/T = FV

Subtract A from each side:
A - A + O/T = FV + A

Cancelling the A's, e have:
O/T = FV - A

Cross multiply the T:
O = T(FV - A)