Move method: Customer.amount_for -> Rental.get_charge
Remove Customer.amount_for call site
Replace temp with query: s/this_amount/rental.get_charge()/g
Extract method: Rental.get_frequent_renter_points
Replace temp with query: s/total_amount/Customer.get_total_charge/
Rewrite get_total_charge loop as comprehension
Replace temp with query: s/frequent_renter_points/Customer.get_total_frequent_renter_points/
Move method: Rental.get_charge -> Movie.get_charge