Answer: 1.1
Step-by-step explanation:
If Sam buys 14 water bottles, he will have spent 18.9, so when you subtract 20 (the limit) from 18.9 (how much money he'll spend on the water bottles) you get 1.1
Use the sum of cubes factoring rule

to transform the left hand side into the right hand side.


Throughout the entire process, the right hand side stayed the same.
On the last step, I used the pythagorean identity.