A body of mass 2kg moves under a force of (2 ^ i + 3 ^ j + 5 ^ k )N...

\overset{\to}{a} = \overset{\to}{F}m = \dfrac{2\overset{^}{i} + 3\overset{^}{j} + 5\overset{^}{k}}{2}

= \overset{^}{i} + 1 . 5\overset{^}{j} + 2 . 5\overset{^}{k}

$\overset{\to}{τ} = \overset{\to}{u}t + \dfrac{1}{2}\overset{\to}{a}{t}^{2}$

= 0 + \dfrac{1}{2}\left(\overset{^}{i} + 1 . 5\overset{^}{j} + 2 . 5\overset{^}{k}\right)\left(16\right)

= 8\overset{^}{i} + 12\overset{^}{j} + 20\overset{^}{k}

$b = 12$