In #21, It's asking you to do simple division and deduce between which two whole numbers the quotient lies. So 20รท3= 6.666... which lies between whole numbers 6 and 7.
In #22, the first place to the right of the decimal is the tenths place. Next to the tenths is the hundredths. Anything 5 to 9 rounds to 1 (a new whole number), 1 to 4 causes the number to remain the same in rounding. So 3.245 rounds to 3.25 to the hundredths place.