Your goal is to get b alone on one side of the equals and get "not b" on the other. In this case, b and h are put together by multiplying. So we do the opposite operation - dividing, to get b and h separated.
A = b * h Put the multiplication operation in the original
A / h = (b * h ) / h Divide by h on both sides
A / h = b The h on the right side simplifies to 1
Thus b = [tex] \frac{A}{h} [/tex]
