The amount of carpet that is needed is equal to the area of the floor. Since the dimensions given are 7 ft long and 9 ft wide, I am going to assume that the room is a rectangle.
The formula for the area of a rectangle is: Area = Length X Width
Area = 7 ft X 9 ft
Area = 63 ft2
Notice that the units on the area are square feet (ft2) since the units are multiplied by each other.