The first step would be to expand the second equation:(x-p)^2+qx^2-px-px+p^2+q
this simplifies to x^2-2px+p^2+q
After this you examine the two equations and identify their similarities such as the x^2 term and the terms with have a single x in them.
From this you can equate the terms which have similar terms (see below)
-2px=-4x and p^2+q=9
Next determine which equation is solvable.
As -2px=-4x only has one variable is it solvable.
Solving this equations gives:
-2px=-4x
cancelling x
-2p=-4
divide both sides by -2
p=2 (save this)
Next use this solution to solve the second equation:
p^2+q=9
substitute p=2
2^2+q=94+q=9
q=5 (save this)
Finally substitute the values for p and q into the original equation
(x-p)^2+q
final answer: (x-2)^2+5
This can be checked by expanding it and ensuring that it does become x^2-4x+9.