Assuming the backyard is rectangular, the area of the real backyard would be 75m².
What is the area of the real backyard?
The formula for the area of a rectangle can be described as follows;
Area = length × width (A = l × w)
According to the question, 3cm represents 5m. Therefore the length of the patio, which is 9cm would represent 15m. The formula for a rectangle is length * width.
So, the area of the rectangle in the above instance is 15m * 5 m = 75m². We can then conclude that assuming the backyard is rectangular, the area of the real backyard would be 75m².