In order to answer your question, you must find the area of the children's pool. Since it is mentioned that the pool's shape is a square and has a side of 15m, you have to find the area of the square, which is s^2. 15m^2 is equal to 225 square meters. Since one square meter costs $17.50, the total cost of covering the pool is 17.50*225, which equals to $3937.50.