Question 1171920
Most of the time:
Equation of the line containing points  (p,v) and (h,k) can be written as 
{{{y-k=((k-v)/(h-p))(x-h)}}}.


You would  substitute your values, simplify, and put into the form of equation you need.


IN YOUR EXAMPLE,  the above is not possible.
YOUR answer to your example is  {{{highlight(highlight(x=8))}}}