Two cylinders A and B, fitted with pistons. A and B contain equal moles of an ideal monoatomic gas at 400 K. Piston in A is free to move, while piston in B is held fixed. Same amount of heat is given to the gas in each cylinder. If the rise in temperature of the gas in A is 42 K, then the increase in the temperature of the gas in B is $ \bigg( \gamma = \large\frac{5}{3} \bigg) $:

Question

$\begin {array} {1 1} (1)\;35\: K & \quad (2)\;42\: K \\ (3)\;70\: K & \quad (4)\;21\: K \end {array}$