Let cm be the edge of variable cube at time
Rate of increase of edge = 3 cm/sec
is positive and = 3 cm/sec
Let be the volume of the cube.
Rate of change of volume of cube = =
=
= cm3/sec
Putting = 10 cm (given),
= cm3/sec
Since is positive, therefore volume of cube is increasing at the rate of 900 cm3/sec.