So, this means we need to solve for x.
So, lets say we have 5 + 7 + x = 25
You start by getting x on its own. Subtract 5 from both sides (to keep it even)
25 - 5 = 20
Then, we're left with 7 + x = 20
Subtract 7 from each side.
20 - 7 = 13
We are then left with:
x = 13
If we plug x in, 5 + 7 + 13 = 25, then we find out that x = 13 is true.
