Which exponential function has an x-intercept a) f(x)=100^x-5 -1 b) f(x)=3^x-4 -2 c) f(x)=7^x-1 +1 d) f(x)=8^x+1 -3

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?