Answer :
There are four possibilities...but first does the problem tell you how many total fish were sold?
If not the possible combinations are:
0 angel and 9 clownfish
2 angel and 6 clownfish
4 angel and 3 clownfish
6 angel and 0 clownfish
If not the possible combinations are:
0 angel and 9 clownfish
2 angel and 6 clownfish
4 angel and 3 clownfish
6 angel and 0 clownfish