There are 2 ways to find xy :
Method 1: (as shown in the suggested solution document, in GoogleSite)
It uses the special products (or algebraic identities) to solve.
Note that we did not need to find x or y value in this method.
In this method, we attempt to solve 2 simple simultaneous equations to find out the values of x and y.
With this, we find xy.
Some of you actually use "Guess and Check" method, where you try to list down possible pairs of integers that can be add together to give 7, followed by check using the other equation.
Do NOT use this method as it opens up many possibilities which would not worth the time to check one by one.