Find the equation of the line that passes through p(7,20) and q the midpoint of r (-3,5) and s (5,11)

First we have to find midpoint of R and S.
We can use formula such for it. and .
We obtained coordinates of point Q 
and 

Now, we can find the line equation using formula y=ax+b. 
We can substitute coordinates of P and Q to this formula and solving system of equation get the answer.

After substituting we obtaind such system


From the system of equation we obtain result
 

Now we can put our resuts to general line equation.