Explanation

(c) $\mathbf{u} = 3\widehat{\mathbf{i}} + 4\widehat{\mathbf{j}},\mathbf{\ a} = 0.4\widehat{\mathbf{i}} + 0.3\widehat{\mathbf{j}}$
Speed $\mathbf{v} = \mathbf{u} + \mathbf{a}t$
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ = 3\widehat{\mathbf{i}} + 4\widehat{\mathbf{j}} + \left( 0.4\widehat{\mathbf{i}} + 0.3\widehat{\mathbf{j}} \right)10$
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ = 3\widehat{\mathbf{i}} + 4\widehat{\mathbf{j}} + 4\widehat{\mathbf{i}} + 3\widehat{\mathbf{j}} = 7\widehat{\mathbf{i}} + 7\widehat{\mathbf{j}}$
$\ \ \ \ \ \ \ \ \ \ \ v = \sqrt{7^{2} + 7^{2}} = 7\sqrt{2}\ unit$