A cylindrical iron rod 8cm high and 6cm in diameter stands In a cylindrical tin until it's depth is 8cm. How far would the level drop when it's rod is removed
hard to say, since we don't know what the level of the contents is.
But the supposed volume submerged is no more than
v = πr^2 h = 72π cm^3
finding the drop in level would entail knowing the diameter of the enclosing tin.
You do have a way of omitting some critical details, there.