Given:
125,000 investment
net asset of the fund was $21.29 back loaded with a loading rate of 3.9%
125,000/21.29 = 5,871.30 shares.
Maya Frankie bought 5,871.30 shares of the Washington Robinson Mutual Fund (Type B.)
The 3.9% loading rate will only be applicable once Maya decides to sell her shares. This is what back loaded means.