Suppose edge of cube =a, time =t, volume =v
∴ V=a3
According to question, at time t increase in rate edge of cube
dadt=7cm/sec
∴ at time t increase in rate volume
dvdt=ddta3
dvdt=dda×a3×dadt
dadt=3a2×7=21a2
∴ Increase in rate of volume of the cube when a=10cm
dvdt=21×102=2100cm3/sec