Explanation:
length = breadth + 5
the perimeter is a rectangle is
2×length + 2×breadth
in our case
2×length + 2×breadth = 74
so, we use the first equation in the second equation :
2×(breadth + 5) + 2×breadth = 74
2× breadth + 10 + 2× breadth = 74
4×breadth = 64
breadth = 16 m
length = breadth + 5 = 16 + 5 = 21 m