How old is a bone if it now .3125 of c-14 when it originally had 80.0g of c-14

42960 years

We are given;

We are required to determine the age of the bone;

Therefore;

0.3125 g = 80.0 g × 0.5^n

3.90625 × 10^-3 = 0.5^n

log 3.90625 × 10^-3 = n log 0.5

Solving for n

n = log 3.90625 × 10^-3 ÷ log 0.5

   = 8

Age of the rock = 5370 years × 8

                          = 42960 years

Thus, the bone is 42960 years old

i think it's c. i'm not sure but i think so.