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 $31 \ cal/kg \cdot ^{\circ}C$ and $1 \ cal = 4.2 \ J$)

• A
  $1.75$
• B
  $1.44$
• C
  $1.15$
• D
  $1.95$