Simplify the expression (y^m+n)/(y^n) to calculate the net growth of an investment, where m is the growth factor for the first phase and n is the growth factor for the second phase.

Using the quotient rule for powers, subtract the exponents when dividing powers with the same base: y^(m+n) / y^n = y^((m+n)−n) = y^m. So the simplified expression is y^m, choice A.

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