You must multiply the two numbers together.
Assuming the room you're measuring the square feet in is in a square formation, you'll only need to multiply the length and the width, which is 10 and 1.5 in this case. Square feet is basically asking for the area of the floor, which is 1.5 * 10 = 15.
Therefore, the amount of square feet in the room is 15 ft.^2
