Given the length of the park = L = 50m
breadth of the park = d = 30 m
for a rectangular field , diagonal d or length of the wall :
d^2 = l^2 +b^2
d^2 = 50 ^2 + 30^2
d^2 = 2500 +900
d^2 = 3400
d = sqr3400
d = 58.30
This means that the length of the wall is 58.3m
