If the distance of the point (a, 2, 5) from the image of the point (1, 2, 7) in the line x/1=(y-1)/1=(z-2)/2 is 4, then the sum of all possible…

If the distance of the point (a, $\displaystyle 2$, $\displaystyle 5$) from the image of the point ($\displaystyle 1$, $\displaystyle 2$, $\displaystyle 7$) in the line $\displaystyle \frac{x}{1}=\frac{y-1}{1}=\frac{z-2}{2}$ is $\displaystyle 4$ , then the sum of all possible values of a is equal to :