Here are two ways of solving this problem.
Method A. Using fractions.
You will need 3 times as much milk, so you need to multiply 3 by 2 3/4.
First, convert 2 3/4 into an improper fraction.
2 3/4 = 2 + 3/4 = 2/1 + 3/4 = 8/4 + 3/4 = 11/4
Now multiply 11/4 by 3.
3 * 11/4 = 3/1 * 11/4 = 33/4
Now convert 33/4 into a mixed numeral.
33/4 = 8 1/4
Answer: 8 1/4
Method B. Using decimals.
You will need 3 times as much milk, so you need to multiply 3 by 2 3/4.
First, convert 2 3/4 into a decimal number.
2 3/4 = 2.75
Now multiply 2.75 by 3.
3 * 2.75 = 8.25
Now convert 8.25 into a mixed numeral.
8.25 = 8 + 0.25 = 8 + 1/4 = 8 1/4
Answer: 8 1/4