The total area of the garden is calculated by the multiplying the length and the width of the garden. In this case, it is equal to 10x15 = 150 ft^2. However, we have to determine the area that is not covered by the stones. The total area of the stepping stones would be 15x1x1= 15 ft^2
Area not covered = 150 - 15= 135 ft^2
