How do you determine an irrational number?

Carter drank 15.75 gallons of water in 4 weeks. he drank the same amount of water each day. a. estimate how many gallons he drank in one day. b. estimate how many gallons he drank in one week. c. about how many days altogether will it take him to drink 20 gallons?

What can you determine about the solutions of this system

Varies inversely with x. if y=8.5 when x=-1 find x when y=-1