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2a-b=5
3a+b=5
b=5-3a
2a-(5-3a)=5
2a-5+3a=5
5a=10
a=2
b=5-3a
b=-1

3p-q=-6
2p+3q=7
q=3p+6
2p+3(3p+6)=7
2p+9p+18=7
11p=-11
p=-1
q=3p+6
q=-3+6=3

a+b+p+q
=2-1-1+3=3