Note to the sample:
The total length of the walls (the perimeter) of the room is 20 m.
One roll of the first type can be cut into pieces to get three vertical 1 meter wide strips, ergo you need 7 rolls of this type, the price equals 700.
A roll of the second type can be cut into pieces to get five 2 meter wide strips, we need 2 rolls, the price is 640.
One roll of the third type can immediately paper 19 meters out of 20, but we cannot use other types and we have to buy a second roll, the price is 1000.