If you want to buy 18 pencils, there are two packages, one is 3 yuan per piece, and the other is 20 yuan in a box of 9 pencils. Which one is cheaper?
要买18支铅笔，有两种包装，一种3元/支，另一种9支一盒包装的共20元，哪一种更便宜？
<result>9</result>