So I got assigned this project for my calc class, and nobody in my group has any idea of what to do with it.

You have been hired by a gallery that has been approached by a dealer who is offering first-purchase rights to a so-called ancient tapestry found outside Athens. The dealer says that the tapestry is some 2,000 years old, loomed in the First Century B.C. However, the gallery has its doubts about the tapestry's age. Their experts were able to obtain a 1 gram sample to conduct tests on. In addition to the elements one would expect to find, they found 190 nanograms of Carbon-14. Assuming the half-life of Carbon-14 is 5,780 years, give as accurate of an estimate as possible of how old the tapestry is.

Based on a graph that was attached (but I don't know how to post it here) we have figured out that the tapestry is less than 400 years old, but we need a more specific number. Any advice?