Apatio floor is shaped like a rectangle with a width of w cm and a length of 21 ft. find an expression that represents the area of the floor.

The answer would be: 21w ft^2

The formula for area of a rectangle is length×width.
For this question,
width = w cm 
length = 21 ft

The first step would be to get the length and width to be the same measurement.
1 ft = 30.48 cm

So you could change both into centimeters.
width = w cm
length = 21 × 30.48 = 640.08 cm

So the expression for the area of the floor would be:
w(640.08)