There were total 2000 people in the survey.
We can multiply relative frequency of any particular category with the total number of people to find the answer for each part.
Part A: How many males surveyed preferred playing sports?
Total Relative frequencies of Males who preferred playing sports = 0.30
Number of Males preferred playing sports = 0.30 x 2000 = 600.
Part B: How many people surveyed preferred to read a book?
Total Relative frequencies of people who preferred reading book = 0.10 + 0.15 = 0.25
Number of people preferred reading book = 0.25 x 2000 = 500.
Part C: How many females were surveyed?
Total Relative frequencies of Females = 0.15 + 0.05 + 0.15 = 0.35
Number of Females surveyed = 0.35 x 2000 = 700.