a) 9 students have dogs.
b) 6 students have cats only
c) 10 students have cats.
From (c) since 10 have cats and 6 have only cats it means 4 students have cats and dogs.
From (a) since 9 students have dogs, and 4 have cats and dogs, it means 5 have only dogs.
Only dogs + Only cats + both cats and dogs + Neither = Total
5 + 6 + 4 + x = 18
15 + x = 18
x = 18 - 15
x =3
B.
