How do find you equivelant expressions?

You'll have to start off by finding the variables. Ex:

3(x + 3) - 2(x + 3) 

As you can see here, the two similar variables are x. By using the distributive property, you will get this: 

3x + 9 - 2x + 6 

Next, you'll want to subtract the two variables, since 2x has a - in front of it: 

1x + 9 + 6 

or 

x + 9 + 6 

Then, you want to add the two numbers without the variable: 

x + 15

Your answer is x + 15. 
Hopefully that helped! :)