What equation represents the amount of caffeine

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?

Astick 2 m long is placed vertically at point b. the top of the stick is in line with the top of a tree as seen from point a, which is 3 m from the stick and 30 m from the tree. how tall is the tree?

How is working backward similar to solving an equation?