Equation: (Not sure if it's the right order...)
468 = 40x + 18(x - 3)
The fee Micheal charges each suscriber is $6
Work:
468 = 40x + 18(x - 3)
468 = 40x + 18x - 54
Mutilpy 18 & x and 18 & 3
468 = 58x - 54
Add 40x amd 18x
468 + 54 = 58x - 54
Add 54 to 468 to have -54 gone in 58x - 54
522 divide by 58 is 9
x = 9
9 - 3 = 6