Question 243957
p+6q=11
4p-q=-6
solve 2nd for q
add 6 to both sides
add q to both sides
4p+6=q
substitute q in first 
p +6 *(4p+6)=11
p +24p+36=11
combine
25p=-25
p=-1
substitute p in first
-1+6q=11
add 1 to both sides
6q=12
q=2

check
4p-q=-6
plug in p and q

4(-1)-(2)=-6
-4-2=-6
-6=-6
ok