Bird population the graph shows the population of a rare species of bird, where (t) represents years since 2009 and N(t) is measured in thousands. when is the population going to be triplicated?

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?