1. **State the problem:** We have a blueprint of a living room with an area of 15 in². The scale is 1 inch : 4 feet. We need to find the actual area of the living room in square feet. 2. **Formula and rules:** The scale means 1 inch on the blueprint corresponds to 4 feet in reality. Since area is two-dimensional, the scale factor for area is the square of the linear scale factor. 3. **Calculate the scale factor for area:** $$\text{Area scale factor} = (4)^2 = 16$$ 4. **Calculate the actual area:** $$\text{Actual area} = \text{Blueprint area} \times \text{Area scale factor} = 15 \times 16 = 240$$ 5. **Interpretation:** The actual area of the living room is 240 ft². This means the living room is 240 square feet in real size.