Assuming there is no teacher:
1.) Since we know that each boy gets one notebook and one pencil, you can calculate total supplies using multiplication and them addition.
Notebook: 1×3 = 3
Pencil: 1×3 = 3
Total: 3+3 = 6
2.) Since we know there are 10 total people and three are guys, we can find how mnay girls there are using subtraction.
10 - 3 = 7 girls
3.) We can find their supplies using the same procedure as the boys just with 7 girls instead.
Notebook: 1×7 = 7
Pencil: 1×7 = 7
Total: 7+7 = 14
4.) To find the entire total, we just add the boys and the girls totals.
6 + 14 = 20
If there is a teacher, then there are 9 students in which 6 are girls.
6× 1 = 6
6 × 1 = 6
6 + 6 = 12 total for girls
and 12 + 6 = 18 total for the class.
I hope this helps!