Consider a mutual fund with two share classes.

Class A Class B

Front$-$end $5\%-$

Back$-$end $-4\%$

$12$b$-1-0\mathrm{.}50\%$

Expense ratio $1\mathrm{.}50\%1\mathrm{.}50\%$

Class B shares back$-$end load fees start at $4\%$ and fall by $1\%$ for each full year the investor holds the portfolio. Assume the rate of return on the fund portfolio net of expenses is $10\%$ annually.

The expected return in Class A is greater than that of Class B if the investment horizon is longer than $\_\_\_\_$ year$($s$).$