Avintage bookstore sold used cd’s and dvds. on tuesday they sold 40 total items if cds were $4 and dvds were $6 each, and sales totaled $180, how many of each item were sold?

Ebuka's monthly rent is $750. if ebuka pays the rent late, his landlord charges 4% interest per week that the payment is late. write a function that gives the total cost r(t), in dollars, of ebuka's rent if he pays it t weeks late.