The total number of students is 55.
That means the total at the bottom of the "Total" column is 55. This means if you have a total of 25 boys, the "Boys" column should have, 15 and 10 (which totals 25).
The row for girls has 25 in row 2, this means Row 2 for boys and girls should have 25 and 10, and that means the second row under "Total" is 35.
Also, row 1 for "Girls" should be 5, since the total in row 1 is 20 and boys in row 1 is 15. Therefore, total for "Girls" should be 5 and 25, which is 30.
Therefore, the missing numbers are;
GIRLS
5
25
30
BOYS
15
10
25
TOTAL
20
35
55