Question

The sum of twice a number and 3 is -9

Answer 1

Let the number be x.

So, it would be 2x + 3 +(-9) = 2x+3-9 = 2x-6.

You can substitute for x for any value.......

Answer 2

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.

`(2x)/(2) = (-12)/(2)`
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. :)