Element X decays radioactively with a half life of 6 minutes. If there are 900 grams of Element X, how long, to the nearest tenth of a minute, would it take the element to decay to 121grams?

Ateacher wanted to buy a chair, a bookshelf, two tables and a desk. she spent $900 for all five items and the chair and the desk combined 70% of her total. if the bookshelf cost $50, how much did each of the tables cost?