There are twelve tubas in the band. And btw you should work on your spelling. I tutor. So if you want my help just message me.
1) I'm not sure what an open operation is.
2) D
3) No
4) Yes
5) D
6) hmm
7) there doesn't seem to be a 6 or 7
8) C
7/10 of 80 is 56
4/5 of 80 is 64
3/4 of 80 is 60
5/8 of 80 is 50
1/2 of 80 is 40
1/4 of 80 is 20
1/10 of 80 is 8
1/8 of 80 is 10
to work these out divide the number by the denominator (bottom number) and multiply by the numerator (top number)