$1, $2, $3 and $4 are economics students who just graduated. They each have a copy of the book "Introduction to Microeconomics" that they are willing to sell. B1, B2, B3 and B4 are new economics students that wish to buy a copy of the book for their introductory economics class. The tables below give the minimum selling prices and maximum buying prices for each student. Minimum Selling Prices Maximum Buying Prices X+$50 B1 $0 $2 X+$75 B2 $50 $3 X+$100 B3 $150 $4 X+$150 B4 $250 Suppose X = $0. What is the market-clearing quantity of books