Easy# Find Parametric Equations for a Line Containing Two Given Points

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Let $L$ be the line that goes through the points $P=(1,2,1)$ and $Q=(3,1,2)$.

In a set of parametric equations for $L$, we have:

$$x=1+2t$$

$$y=2-t$$

$$z=1+ct$$

What is the value of $c$?