Number of male students with X hair + Number of female students with X hair = Total number of students with X hair
(where X is any hair color)
Number of Y students with brown hair + Number of Y students with blonde hair + Number of Y students with hair of another color = Total number of Y students with any hair color
(where Y is either male or female)
Total number of male students + Total number of female students = Total number of students with brown hair + Total number of students with blonde hair + Total number of students with hair of another color = Total number of students overall
There are 39 total students. 21 of them are female. So 39 - 21 = 18 of them are male.
13 students had brown hair. 11 had blonde hair. So 39 - 13 - 11 = 15 had hair of another color.
13 students had brown hair. 5 male students had brown hair. So 13 - 5 = 8 female students had brown hair.
11 students had blonde hair. 4 female students had blonde hair. So 11 - 4 = 7 male students had blonde hair.
18 students are male. 5 had brown hair and 7 had blonde hair. So 18 - 5 - 7 = 6 of them had hair of another color.
21 students are female. 8 had brown hair and 4 had blonde hair. So 21 - 8 - 4 = 9 of them had hair of another color.
Put all this into the table (see attached).