Determine the number of zeros of the polynomial function.
1. f (x) = x - 6
2. g (x) = x2 − 2x − 8
3. h (t) = t2 − t5
4. f (x) = x8 + x9
5. f (x) = (x − 8)3
6. g (t) = (2t − 1)2 − t4