Does anyone know what the addition method is, and how do i solve this?

-x - 7y = 18
4x + 7y = -30

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?

Write the percent as a fraction or mixed number in simplest form. 0.8%

Construct a box plot to represent the ages of the actors in a play. step 1: arrange the numbers in order from lowest (on the left) to highest. 24 18 30 26 24 33 32 44 25 28