C-14 has a half life if approximately 5700 years how many years will it take for the radioactivity of a sample to reach one-fourth of its original amount
a. 1425
b.5700
c.11400
d. 22800

This is an easy half-life problem.
Every half-life, a substance loses half its radioactivity.  So, after 2 half-lives, a substance will have a quarter of its radioactivity.
2 * 5,700 = 11,400 years
answer is C

It is 198,87032,750 + 375 = 33145 so, we take the 6% and we make it a decimal (0.6) and multiply that, then that is your answer