Tom and his friend Edward are seeking to join a gym. Tom saw on television that Platinum Gym was having a grand opening in a few months. Tom is considering a membership at Platinum gym. Platinum gym charges a one-time registration fee of $60, and membership is $20 a month. Tom's best friend Edward says he plans to join Super Fit because Super Fit only charges $10 a month but has a one-time registration fee of $150.

write an expression to represent the membership cost of platinum gym for x months