The sum of 15 and the product of 5 and v

The equation in words would be 15 + 5v = 0
To figure out the solution you would subtract 15 from both sides. 
15-15+5v=0-15
This equals: 5v=-15
To get the v by itself divide both sides by 5. 
This gets v on one side (the left) and -15 divided by 5. 
-15 divided by 5 is -3. 
So the solution would be v=-3