请教一道陈向东的数学题

BERYL1986

a home owner must pick between paint A,which costs 6 per liter, and paint B,which costs 4.5 per liter. Paint B takes one-third longer to apply than paint A.If the homeowner must pay the cost of labor at the rate of 36 per hour,which is the two paints will be cheaper to apply?
(1) the ratio of the area covered by one liter of paint A to the area covered by paint B is 4:3.
(2)pait Awill require 40 liters of paint and 100 hours of labor.
这题的答案是E，我怎么觉得是A啊。设A要x liters,h hours
那么A的成本就是6x+36h
B的成本是4.5x*4/3+36h*4/3=6x+36h*4/3
显然A比B便宜啊。

大家告诉我是我错了还是答案错了。
谢谢了！

BERYL1986

怎么没人帮我回答下呢