Uncle Zhang used reed mats with a length of 2 meters and a width of 1 meter to form the largest cylindrical grain storage in the year before last. The volume of grain storage is how many times that of the previous year.
张大伯前年用长2米、宽1米的苇席围成一个容积最大的圆柱形粮囤，去年改用长3米、宽2米的苇席围成一个容积最大的圆柱形粮囤，去年粮囤的容积是前年的多少倍．
<result>4.5</result>