Centre of Mass, Momentum and Collision · Collisions

In a perfectly inelastic collision, two spheres made of the same material with masses 15 kg and 25 kg, moving in opposite directions with speeds of 10 m/s and 30 m/s, respectively, strike each other and stick together. The rise in temperature (in $^\circ$C), if all the heat produced during the collision is retained by these spheres, is:

(specific heat of sphere material 31 cal/kg. $^\circ$C and 1 cal $= 4.2$ J)