Area of the rectangle = L X W
Area of the rectangle = 4 X 2
Area of the rectangle = 8 inches
If the drawing is 1/5 of the actual air conditioning unit, then you multiply the reciprocal which is 5 times the area of the drawing. When you want to enlarge it has to be a whole number. When you want to reduce you multiply by a fraction.
So 8 inches X 5 = 40 inches is the actual area of the unit.