The function for radioactive decay is R(t)=R

_{0}(1/2)

^{t/h}, where R is the radioactivity/gram of carbon-14 at time t after death, R

_{0}is the radioactivity/gram of carbon at the time of death, and h is the half-life of carbon-14. The half-life of carbon-14 is 5370 years. After 3000 years, how much carbon-14 radioactivity/gram remains in a dead tree?

So far I've set up the equation:

R(t)=R

_{0}(1/2)

^{3000/5370}

But how are you supposed to solve for R(t) when you have 2 unknowns?