The possible outcomes for tossing a coin four times are shown below.

1. t-t-t-t 5. t-h-t-t 9. h-t-t-t 13. h-h-t-t
2. t-t-t-h 6. t-h-t-h 10. h-t-t-h 14. h-h-t-h
3. t-t-h-t 7. t-h-h-t 11. h-t-h-t 15. h-h-h-t
4. t-t-h-h 8. t-h-h-h 12. h-t-h-h 16. h-h-h-h
tails = t heads = h

if a coin is tossed four times, what is the probability of getting exactly zero heads?