The floor of a conference room in Mingde Primary School is a rectangle with a length of 9 meters and a width of 6 meters. Two kinds of porcelain tiles of the same quality are sold in the market: 10 yuan for each tile with an area of 0.25 square meters, and 18 yuan for each tile with an area of 0.36 square meters. If you want to buy one of these tiles to cover this meeting room, please help the principal do the math, which one is more economical to buy?
明德小学一间会议室的地面是长9米，宽6米的长方形．市场上出售两种质量相同的瓷方砖：面积0.25平方米的瓷方砖每块10元，面积0.36平方米的瓷方砖每块18元．如果要买其中一种瓷方砖铺满这间会议室，请你帮校长算一算，买哪一种砖更省钱？
<result>0.25</result>