Pure platinum is too soft to be used in jewelry because it scratches easily. To increase the hardness so that it can be used in jewelry, platinum is combined with other metals to form an alloy. To determine the amount of platinum in an alloy, a 7.637 g sample of an alloy containing only platinum and cobalt is reacted with excess nitric acid to form 1.31 g of cobalt(II) nitrate. Calculate the mass percent of platinum in the alloy.