Given the following information, how many years have passed since the rock was formed?

Carbon-14 has a half-life of 5,730 years. This means that only half the carbon-14 that was trapped in a rock when it formed will remain after 5,730 years. After another 5,730 years, only one-fourth of the original amount of carbon-14 will remain. A scientist finds a rock that contains one gram of carbon-14. The scientist estimates that the rock originally contained eight grams of carbon-14.