You dissolve a crystal of apatite and spike it with a Uranium spike of known composition. Use the information given below to calculate the concentration of Uranium in that crystal. Natural abundance of 238U = 99.7%; natural abundance of 235U = 0.3% Abundance of 238U in spike = 1.2%; abundance of 235U in spike = 98.8% You add 2g of a that spike, which contains 5.6 ug/g of Uranium enriched in 235U, to 12g of dissolved apatite. The apatite that you crushed and powdered weighed 0.14g. You mix the dissolved apatite with the spike solution and then pass the mixed solution through ion exchange columns to isolate the Uranium. You then load it on a filament and measure isotopic ratios using TIMS. The ratio of 238U/235U that you measure = 2.1. What is the concentration of U in the apatite?