a cubic block of ice is melting at an unnaturally controlled

a cubic block of ice is melting at an unnaturally controlled rate. Its volume is changing at the constant
rate of -75 cubic cm per minute. When the length of each of its sides is 5 cm, how fast is this length changing?

we have, Volume = V = l^3 differentiating , we have, dV/dt = 3 l^2 dl/dt -75 = 3 x 5^2 dl/dt dl/dt = -1 cm /minute