Solution:
Let the length of the shorter side be x metres.
Thus the length of the longer side=(x+30) m
Length of the diagonal=(x+60)m
Each angle of a rectangle=90 degrees
By Pythagoras Theorem, (diagonal)2=(shorter side)2+(longer side)2
(x+60)2 = x2+(x+30)2
x2-60x-2700=0 => (x+30)(x-90)=0 => x=-30 or x=90
As the length of a side cannot be negative,the length of the shorter side = 90 m.
Thus the length of the longer side=120 m