Scientists calculate that the average temperature of the earth is increasing at a rate of 0.12 degrees a year. This situation can be modeled by what type of function?

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?