"Without using a calculator" suggests you are supposed to have memorized the square roots of 2 and 3 to at least 3 decimal places. That is, you know
21. √8 = √(2²·2) = 2√2 ≈ 2.83 . . . . about 4/5 of the distance between 2 and 3
22. √75 = √(5²·3) = 5√3 ≈ 8.66 . . . about 2/3 of the distance between 8 and 9
