Gabby 's gym charges members an initial joining fee of $300 plus $50 per month. so members can calculate how much they have paid to the gym using the formula c= 50m+30, where m is the number of months they have been members. will's workout charges $65 per month with no initial fee. so members of will's can calculate their charges using formula c=65, where m is the number of months they have been members.