The first coat of paint for the outside walls of a building requires 1 of paint

The first coat of paint for the outside walls of a building requires 1 ℓ of paint for each 10 m² of wall surface. The second coat requires 1 ℓ for every 15 m². If the paint costs $3.50 per liter, what will be the cost of two coats of paint for the four outside walls of a rectangular building 20 m long, 15 m wide, and 6 m high?