Uranium-238 (U-238) has a half-life of 4.5 billion years. Geologists find a rock containing a mixture of U-238 and lead, and determine that 85% of the original U-238 remains; the other 15% has decayed into lead. How old is the rock? The rock is billion years old. (Round to three decimal places as needed.)Find the present value of $9000 payable at the end of 3 years, if money may be invested at 7% with interest compounded continuously. The present value of $9000 is $ (Round to the nearest cent as needed.)