Finding a sequence of equations to equal another equation [closed]

I'm wondering what kind of problem space this might be?

Lets say I have an equation eg $x + y = Q$

Then I have a series of other equations involving $x$ and $y$. how might I determine what sequence of equations to use to get the same value of $Q$ with constraints?

Eg:$x = 5 \\ y = 10 $

1. $x = x_1\cdot 5 $
2. $y = y_1 - 20$

So then you would get$ 5 \cdot 5 + 10 - 20 = Q$Following step 1 then step 2