An explosion breaks a rock into three parts in a horizontal plane. Two of them go off at right angles to each other. The first part of mass 1 kg moves with a speed of $12 ms^{–1}$ and the second part of mass 2 kg moves with $8 ms^{–1}$ speed. If the third part files off with $4 ms^{–1}$ speed, then its mass is -

Question

( A ) 5 kg
( B ) 7 kg
( C ) 17 kg
( D ) 3 kg