Respuesta :

let x = # of monthly fee
f(x) = (50x + 30)/x

average cost will be below 56 for how many months?
(50x + 30)/x = 56
50x + 30 = 56x
56x - 50x = 30
6x = 30
  x = 5

answer:
the average cost will be below $56 for 5 months