Two bodies of 6 kg and 4 kg masses have their velocity $5\widehat{\mathrm{i}}-2\widehat{\mathrm{j}}+10\widehat{\mathrm{k}}$ and $10\widehat{\mathrm{i}}-2\widehat{\mathrm{j}}+5\widehat{\mathrm{k}}$ respectively. Then the velocity of their centre of mass is

• A

  $5\widehat{\mathrm{i}}+2\widehat{\mathrm{j}}-8\widehat{\mathrm{k}}$

• B

  $7\widehat{\mathrm{i}}+2\widehat{\mathrm{j}}-8\widehat{\mathrm{k}}$

• C

  $7\widehat{\mathrm{i}}-2\widehat{\mathrm{j}}+8\widehat{\mathrm{k}}$

• D

  $5\widehat{\mathrm{i}}-2\widehat{\mathrm{j}}+8\widehat{\mathrm{k}}$