GMAT(Problem Solving)対策問題


A certain store sells pens and erasers. all pens are sold at an qeual price, and all erasers are sold at an qeual price. It costs 840 yen to buy 5 pens and 3 erasers. It costs 560 yen to buy 2 pens and 4 erasers. How much less does the store charge for a pen than for an eraser.