Let x represent the base tax. If the total fare charged to a customer comes to $765.71 including 5.5% sales tax, it means that
5.5% of x + x = 765.71
5.5/100 * x + x = 765.71
0.055 + x = 765.71
1.055x = 765.71
x = 725.79
The base fee is 725.79
If the travel agent receives a 6% commission on the base fare of a customer, it means that the commission received is
6/100 x 725.79
= 43.55