intriguing question..involving logs and exponential decay/growth?

Carbon taken from an old animal skeleton contains 3/4 as much radioactive carbon14 as carbon taken from a present day bone. How old is the animal skeleton? (the half-life of carbon 14 is 5760 years)

**halflife: the time required for something to fall to half its initial value **

let P represent the amount of radioactive carbon 14 from a present day bone

i have 2 problems with this question.

i know 1/2P= P(x)^5760, but what adjustment will be made to 5760 since we are dealing with 3/4P instead of 1/2P?

and how do you isolate x after that?

thanks in advance