Question 3
Tiến, Sơn and Đức start with the same amount of money. Tiến buys 3 pencils and 4 notebooks and has 7 dollars left. Sơn buys 3 pencils and 3 notebooks and has 28 dollars left. Đức buys 1 pencil and 4 notebooks and has 21 dollars left. How many dollars more does one notebook cost than one pencil?
