Algebra in geometry please help me

An arc subtends a central angle measuring 7pi/4 radians what fraction of the circumference is this arc?

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?

Which of the following expressions cannot be simplified to x – 2?