Let us say the shorter side of the rectangle is x m.
Then, larger side of the rectangle = (x + 30) m
Diagonal of the rectangle =$\sqrt{x^{2}+(x+30)^{2}}$
As given, the length of the diagonal is = x + 30 m
Therefore,
$\sqrt{x^{2}+(x+30)^{2}}$=x+60
⇒ $x^{2}2 + (x + 30)^{2}$ = $(x + 60)^{2}$
⇒ $x^{2}+ x^{2} + 900 + 60x $= $x^{2} + 3600 + 120x$
⇒$ x^{2} – 60x – 2700$ = 0
⇒ $x^{2} – 90x + 30x – 2700$ = 0
⇒ x(x – 90) + 30(x -90) = 0
⇒ (x – 90)(x + 30) = 0
⇒ x = 90, -30
However, the side of the field cannot be negative. Therefore, the length of the shorter side will be 90 m, and the length of the larger side will be (90 + 30) m = 120 m.