Remark
Question B is a bit of a guess, but A is pretty straight forward.
A
Let P = Platinum Gym's income (total)
Let M = Platinum Gym's Registration Fee.
Number of people who received free membership registrations = 50
The total income from anyone who had to register was
P = (124 - 50)*M
P = 74 * M
B
Monthly Fee = MF
n = number of months = 6
c = customer base = 124
Equation
P = Registration Fee (found in A) + n * c * MF
Solution
P = 74*M + 6*124*MC
P = 74M + 744*MC
The question is, do you count the registration fee at the beginning or not? I would.