The question to be solved is.
The aim here is to eliminate one of the variables from the equations by performing operations on them. We then have a one variable equation which we can solve. Then substitute this value into either one of the 2 given equations and solve for the other variable.
I have labelled the equations to assist.
Note that in (1) there is a - 7q and in (2) there is + 7q
Adding these together will eliminate the variable q, which is what we want.
Add (1) and (2) together term by term on both sides.
Now substitute p = 3 into (1) or (2). I'll choose (2) you can perhaps try (1).
Hope this helps.