Find the following expressions if $\mathbf{a} = 2\mathbf{i} - 5\mathbf{k}$ and $\mathbf{b} = \mathbf{i} +\mathbf{j} - 2\mathbf{k}$.

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1. $|\mathbf{a}| =$

2. $\mathbf{a}+\mathbf{b} =$

3. $\mathbf{a}-\mathbf{b} =$

4. $3\mathbf{a}+4\mathbf{b} =$

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