Find the magnitude of a given by `veca=(hati+3hatj+hatk)xx(-hati+3hatk)`

Explanation

To find the magnitude of the vector \(\vec{a} = (\hat{i} + 3\hat{j} + \hat{k}) \times (-\hat{i} + 3\hat{k})\), we will follow these steps:

### Step 1: Set up the cross product
We need to calculate the cross product of the two vectors:
\[ \vec{a} = \hat{i} + 3\hat{j} + \hat{k} \]
and
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