The unit "troy ounce" is often used for precious metals such as gold (Au) and platinum (Pt) (1 troy ounce= 31.103 g). (a) A gold coin weighs 2.41 troy ounces. Calculate its mass in grams. (b) Is a troy ounce heavier or lighter than an ounce (1lb =16 oz; 1lb =453.6 g)?