Answer:

Volume of the well = Volume of the embank

Volume of the cylinder = Volume of the embank

Cylinder :

Height/depth, h = 15 m

Volume V = πr²h

= × ×

= m³

Embank:

Let the height of the embank = h m

Inner radius ‘r’ = Radius of well = 7 m

Outer radius, R = inner radius + width

= m + m = m

Area of the base of the embank = (Area of outer circle) – (Area of inner circle)

= πR² – πr²

= π(R² – r²)

= m²

∴ Volume of the embank = Base area × height

= × = m³

∴ m³ = m³