Final answer:
The area of the other side of the rectangular playground, with one side measuring 4 ft and a total area of 2500 ft², is 625 ft². This is calculated by dividing the total area by the length of the known side.
Step-by-step explanation:
If the area of a rectangular playground is 2500 ft² and one side measures 4 ft, then the other side can be found by dividing the total area by the length of the one known side. The formula for the area of a rectangle is Area = length × width. So, if one side is 4 ft and the total area is 2500 ft², then the other side must be:
Area ÷ length = width
2500 ft² ÷ 4 ft = 625 ft
So, the area of the other side of the playground is 625 ft², which corresponds to option a) 625 ft².