Question

How many solutions does the equation 6s − 3s − 9 = −2 + 3 have?
Only one
None
Two
Infinitely many

Answer 1

6s - 3s - 9 = -2 + 3
3s - 9 = -2 + 3
3s - 9 = 1
3s = 10
s = 10/3
s  = 3.3333

The equation has 1 solution. 

Answer 2

To see how many solutions it has, you first have to solve it.

6s − 3s − 9 = −2 + 3
First combine like terms.
3s - 9 = 1
Add 9 to both sides.
3s = 10
Divide both sides by 3.
s = 3.33

The answer is 
A. Only one