Plz give the calculation of CLASS B in detail I m so confused with it thanks

The Investments Fund sells Class A shares with a front-end load of 6 percent and Class B shares with other charges of .5 percent annually as well as backend load fees that start at 5 percent and fall by 1 percent for each full year the investor holds the portfolio (until the fifth year). Assume the portfolio rate of return net of operating expenses is 10 percent annually. If you plan to sell the fund after four years, are Class A or Class B shares the better choice for you? What if you plan to sell after 15 years?