A well is dug 20 m deep and it has a diameter of 7 m.

Height of the well = h m = 20 m

Diameter of the well = d m =7 m

Radius of the well = r m = 3.5 m

Volume of the well = πr2h = $\frac{22}{7}(3.5)^{2}(20) \mathrm{m}^{3}=770 \mathrm{~m}^{3}$

Volume of the well = Volume of the rectangular plot

Length of the rectangular plot = 22 m

Breadth of the rectangular plot =14 m

Volume of the rectangular plot = 770 m3 = (Length×">×× Breadth ×">××Height) of the rectangular plot

Height $=\frac{770}{22 \times 14}=2.5 \mathrm{~m}$

Thus, the height of the platform is 2.5 m.