Given, $ \vec{A}=\hat{6}+7\hat{j}+0\hat{k} $ and $ \vec{B}=3\hat{i}+4\hat{j}+0\hat{k} $ Sum of two vectors $ =\vec{A}+\vec{B} $ $ =(6\hat{i}+7\hat{j}+0\hat{k})+(3\hat{i}+4\hat{j}+0\hat{k}) $ $ =(6\,+3)\,\hat{i}+(7+4)\hat{j}+(0+0)\hat{k} $ $ =9\hat{i}+11\hat{j} $ Therefore, magnitude of the sum of twovectors $ =\sqrt{{{(9)}^{2}}+{{(11)}^{2}}} $ $ =\sqrt{81+121} $ $ =\sqrt{202} $