Two cylinders A and B fitted with pistons contain equal amount an ideal diatomic gas at 300 K. Piston of A is free to move and piston B is fixed. Same amount of heat is given to the gases in the two cylinders. Temperature of the gas in cylinder A increases by 30 K. Then, increase in temperature of the gas in the cylinder B is ( $\gamma$ 1.4 for diatomic gas)

$\begin {array} {1 1} (1)\;24\: K & \quad (2)\;36\: K \\ (3)\;54\: K & \quad (4)\;42\: K \end {array}$

(4) 42 K