Confused on how the equation for finding the area of gym not including the closet. (image)

Find find the area of the closet and subtract it from the area of the (gym and closet)
Area of gym and closet = L x w = 5 x 4 = 20
Area of the closet = L x w = 2 x 1 = 2
Area of gym only = (gym and closet) - closet
= 20 - 2
= 18
Answer: 18 cm²