Pls help me with this question and if you don't know, pls don't answer. thank you!

Write numerical coefficient of y² in the expression 2x² - 15xy – 7y²

Put the equation in slope intercept form by solving for y

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?