The radius of a sphere is increasing at a rate of $\"\"$ mm/sec.

Therefore, $\"\"$ mm/sec.

Diameter is $\"\"$ mm.

Radius is half of the diameter $\"\"$ mm.

The volume of the sphere is $\"\"$ .

$\"\"$ .

Differentiate on each side with respect to $\"\"$ .

$\"\"$

$\"\"$ .

Substitute $\"\"$ and $\"\"$ in above expression.

$\"\"$

Volume of the sphere increases at rate of $\"\"$ mm³/sec.