Can someone please explain to me how this works?

An advertising firm has an old computer that can prepare a whole mailing in 6 hours. with the of newer model the job is complete in 2 hours. how long would it take the newer model to do the job alone?

Write an algebraic expression to match each statement a. four less than 8 times a number b. twice the difference of a number and six c. nine from a number squared

Yesterday, george drank 1 small bottle and 2 large bottles, for a total of 1,372 grams. the day before , he drank 1 small bottle and 1 large bottle, for the total of 858 grams. how many grams does each bottle hold?