A well with 10m inside diameter is dug 84 m deep Earth

SOLUTION

Diameter of the well = 10 m



$\therefore$ Radius (r) = $\frac{10}{2}$= 5 m
Depth (h) = 8.4 m
$\therefore$ Volume of earth dug out =  $\pi r^{2}h$ 
=$\frac{22}{7}\times 5\times 5\times 8.4m^3=660m^3$
Width of embankment = 7.5 m
$\therefore$ Outer radius (R) = 5+7.5 = 12.5 m
Area of embankment = $\pi (R^2-r^2)$
= $\frac{22}{7}\left[\right(12.5{)}^2-5^2]$
= $\frac{22}{7}(12.5+5)(12.5-5)$
= $\frac{22}{7}\times 17.5\times 7.5m^2=412.5m^2$
Let h be the height of embankment, then 
Voulme of embankment = 412.5 h = 660 $\Rightarrow h=\frac{660}{412.5}m$ 
$\therefore 412.5h=660\Rightarrow h=\frac{660}{412.5}\times h{m}^3$
$\Rightarrow$ h =  1.6019 m = 1.6 m