The x will represent the number you are trying to find. The sum with 3 will get to the total which is -9.
2x + 3 = -9
Subtract 3 from both sides.
2x + 3 = - 9
- 3 - 3
Becomes...
2x = -12
Divide both sides by 2 so that x is alone.
[tex] \frac{2x}{2} = \frac{-12}{2} [/tex]
Now is looks like this:
x = -6
The number is -6.
Check:
2(-6) + 3
-12 + 3 = -9
It's correct.
Hopefully, this was understandable. :)