Explanation:
the perimeter of a rectangle is
2×length + 2×width
so our inequalities are
2×length + 2×width <= 140 m
length + width <= 70 m
width <= 24 m
let's assume for a moment that width = 24.
and we get
length + 24 <= 70
length <= 46 m
or general
length <= 70 - width
with maximum width (24 m), length <= 46m
with a minimum width (e.g. 1 m), length <= 69
so, overall, 0 m < length < 70 m (I assume width = 0 or length = 0 are not valid).