Explanation:
breadth = 21 m
length = 63 m
w = 21 feet
l = 63 feet
l = 3w
P = 2(l + w)
168 = 2(l + w) : 2
84 = l + w
replace l
84 = 3w + w
4w = 84
w = 84 : 4
l = 3×21 feet
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