I like to reduce everything by half if I don't already know the answer.

It just so happens that is the reduced fraction. 
All I did was halve 18, which is 9, and halve 34, which is 17. 
 
        
             
        
        
        
Answer: About 6.71 units
Step-by-step explanation:
You use the distance formula:  .
.
Assign the the two points to the variables:

Substitute them in the formula:

And solve it:

 
        
                    
             
        
        
        
The awnser is 20 quarters