Answer: Rectangle ABCD represents the swimming pool.
Rectangle EFGH represents the swimming pool surrounded by the concrete border.
AB = CD = 50 m and BC = DA = 25 m
EF = GH = 50 + 2x3 = 56 m and FG = HF = 25 + 2x3 = 31 m
So, perimeter of outer rectangle i.e. rectangle EFGH = 2(EF + FG) = 2(56 + 31) = 174 m.
Area of the outer rectangle = 56 x 31 = 1736 m%5E2.
Area of the inner rectangle = 50 x 25 = 1250 m%5E2.
So, area of the concrete border = 1736 - 1250 = 486 m%5E2.
Step-by-step explanation: Image shown.