Help meh I am severely confused or I’m just not smart

The formula for circumference is 2pi r so you multiply 2 times pi times the radius (half of the diameter)
For example the first one has a diameter of six so it would have a radius of 3. You formula would then be 2 x 3.14 x 3 which equals 18.84 so your circumference is 18.84

a. about 1/2 gallon per day

b. about 4 gallons per week

c. 36 days to drink 20 gallons

Step-by-step explanation:

Given that Carter drank 15.75 gallons of water in 4 weeks, that is 28 days (4 x 7).  In order to find the number of gallons he drank in one day, divide the total number of gallons by the number of days:  15.75/28 = .5625 gallons.  If you are estimating, that is about a half gallon each day.  

Since the total number of weeks was 4, in order to find the number of gallons in one week, you divide the total gallons by 4 weeks:  15.75/4 = 3.9375.  If you are estimating, that is about four gallons each week.

In order for Carter to drink 20 gallons, you can take the amount of gallons and divide by the number he drinks daily:  20/0.5625 = 36 days.