Simply put multiply 15 by 40 to get the square footage. This would be 600 square feet.
15 * 20 = 300 square feet.
If you mean 75 feet x 15 feet then the square footage is 1,125 square feet.
15 feet x 15 feet = 225 square feet.
375
The question does not give the units of measurement for the room's size. Assuming they are feet, the square footage is 12*15 = 180 square feet.
225 square feet
240 square feet. (16 x 15 = 240)
20 x 15 = 300 square feet.
225 square feet (15 x 15 = 225).
20ft * 15ft = 300 square feet.
15 *60 = 900