1. The answer is 16^2, so B.
16 x 16 = 256
2. The answer is 17, so B.
Some of the factor of 68 are: 1, 2, 4, 17, 34 and 68.
3. The answer is 15, so B.
Only 15 is composite since it contains more than a factor, which are 3 and 5. The rest of the numbers are prime since they only contain a factor.
4. The answer is 2^2^3^7, so B.
The factor tree:
84
2 x 42
2 x 2 x 21
2 x 2 x 3 x 7
Hope this helps! :)
