Explanation

(b) $\overrightarrow{v} = \overrightarrow{u} + \overrightarrow{a}t \Rightarrow \overrightarrow{v} = 3\widehat{i} + 4\widehat{j} + (0.4\widehat{i} + 0.3\widehat{j}) \times 10$
$v = 3\widehat{i} + 4\widehat{j} + 4\widehat{i} + 3\widehat{j} = 7\widehat{i} + 7\widehat{j}$
$\Rightarrow \left| \overrightarrow{v} \right| = 7\sqrt{2}$ units