I can't seem to work out the answer. Help would be appreciated.

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Q:

Find an equation of the plane, in the form $\displaystyle \bold r \bold . \bold n = p$, which contains the line $\displaystyle l$ and the point with the position vector $\displaystyle \bold a$ where $\displaystyle l : \bold r = t ( 2 \bold i + 3 \bold j - \bold k)$, $\displaystyle \bold a = \bold i + 4 \bold k$.

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Thanks in advance.

P.S. The answer is $\displaystyle \bold r \bold . (4 \bold i - 3 \bold j - \bold k) = 0$