If you are not familiarized with this method, do the following:
1) Write in the intersection area the number of students who take both French and Spanish (3).
2) Write on the first circle for the area without the intersection the number of students who take French but not Spanish too (8 - 3 = 5)
3) Do the same for the other circle writing the number of students who take only Spanish (12 - 3 = 9)
4) Add the numbers in all 3 areas. You will find that 5 + 3 + 9 = 17 (the same)
Now we are looking the students that have neither French or Spanish. Hence:
n(neither) = n(all students) - n(F or S)
n(neither) = 30 -17
n(neither) = 13
Hence 13 students have neither French nor Spanish