The partially filled contingency table gives the frequencies of the data on age (in years) and sex from the residents of a retirement home.


60-69
70-79
Over 79
Total
Male
15
4
5

Female
5
7
4

Total


What is the relative frequency for persons in the age group 60-69 ?
a.2/3

b.1/4

c.1/2

d.1/3