If you don't double check your answers by substituting them back into the original equation, you may be introducing extraneous solutions into the problem which is why you should always check to confirm your answer is accurate. I hope this helps! :)
So you distrubute and get
-2p-8+2-3+5p
add like terms
3p-9
ANSWER: 3p-9
answer is (-7,-9)
step by step:-
S is the midpoint of RT so ,
s=
, 
, 
, 
R= (-7,-9)