A bookstore sells paperback fiction books in excellent condition for $2.50 and in fair condition for $0.50. Write an expression for the cost of buying 'x' excellent-condition paperbacks and 'f' fair-condition paperbacks........ A) 2.50x + 0.50f...... B) 3.00 (x + f)..... C) 2.50f + 0.50c.... D) 3.00 + x+f