If the image of point $\left(2, 1\right)$ with respect to the line mirror be $(5, 2)$, then the equation of the mirror is,

Find the inclination of a line $l$ in the following figure. [Answer without degree symbol]

Find the inclination of a line $l$ in the following figure

The slope of a line joining $P\left(6, k\right)$ and $Q(1-3k, 3)$ is $\raisebox{1ex}{$1$}\!\left/ \!\raisebox{-1ex}{$2$}\right.$. Find mid-point of $PQ$, using the value of $\text{'}k\text{'}$.