Help me please I beg of you

Afootball is throw by a quarterback to a receiver

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?

When you find the area of a triangle do you use in. or in2