CHEMISTRY QUESTION:!!! PERCENT YIELD?

A 2.197 g sample of limestone was dissolved in HCl and all the calcium in the limestone was converted to Ca2+(aq). The solution was treated with excess ammonium oxalate, (NH4)2C2O4(aq), and it was found that 2.440 g of calcium oxalate, CaC2O4(s) was precipitated. Calculate the percentage of calcium in the limestone. (Please give your answer to 4 significant figures)