Answer:
A) l = 10m
B) l = 15m
Explanation:
A) The area of a square courtyard is 100m2. In order to calculate the length of one side of the courtyard you use the formula for the area of a square:

Then, one side of the courtyard has a length of 10m.
B) The are of the second courtyard is 225m^2. You use the same procedure of the previous point:

The length of one side is 15m