A 50.0 g block of copper whose temperature is $400 \mathrm{~K}$ is placed in an insulating box with a $100 \mathrm{~g}$ block of lead whose temperature is $200 \mathrm{~K}$. (a) What is the equilibrium temperature of the twoblock system? (b) What is the change in the internal energy of the system between the initial state and the equilibrium state? (c) What is the change in the entropy of the system? (See Table $18-3 .)$