Let h1 be the height of circular tank Then
Volume of circular tank= Volume of embankment=πr2h1.....(1)
Height of embankment, h2=3.5 m
Inner radius of embankment, r1=7m
Outer radius of embankment, r2=8m
∴ Volume of embankment=πr21h2−πr22h2
=π(82×3.5−72×3.5)
=π(224−49×3.5)=52.5π
Substituting in (1) we get
π×72×h1=52.5π
or h1=52.549=7.57×22=1514m