I think p=4
How I solved it: 
5(-2)+2p+2(-1)=2p
-10+2p+-2=2p So cross out last 
 -2p -2p 2p:)
= -10+2p+-2
 +10 +10 Cross out the 10
= 2p=8
= divide both sides by 2p
= 2p/2= 8/2
= cross out the 2.
= which leaves 
= p=4 we get 4 because we divide 8 to 2:)
I don’t know if I’m right but yea...