The monthly bill mainly consists of two parts: the standard charge of $60 per month, and the cost of additional data consumed by the user after the first 1000 megabytes at $0.05 per megabyte. Translating this into an equation:
Monthly bill = standard charge + additional charge
where: standard charge = $60.00
m = megabytes
additional charge = $0.05(m - 1000)
monthly bill = $60.00 + $0.05(m - 1000)