An impulse of 6m $\vec{j}$ is applied to a body of mass m moving with velocity ($\vec{i} + 2\vec{j}$). The final velocity of the body will be

$\vec{i} + 8\vec{j}$

Impulse = Change in linear momentum 

$\vec{\Delta p} = \vec{p_f} - \vec{p_i}$

$\vec{p_f} = \vec{p_i} + \vec{\Delta p} = m\vec{i}+2m\vec{j}+6m\vec{j}$

⇒ m$\vec{v_f} = m\vec{i}+8m\vec{j}$

⇒ $\vec{v_f} = \vec{i}+8\vec{j}$