Prep数学题，求解，谢谢啦

yizyang

The cost of a square slab is proportional to its thickness and also proportional to the square of its length.  What is the cost of a square slab that is 3 meters long and 0.1 meter think?

(1) The cost of a square slab that is 2 meters long and 0.2 meter thick is $160 more than the cost of a square slab that is 2 meters long and 0.1 meter thick.
(2) The cost of a square slab that is 3 meters long and 0.1 meter thick is $200 more than the cost of a square slab that is 2 meters long and 0.1 meter thick.


我选的是两个在一起才可以，但是答案竟然是每个都是sufficient.  请问这是为什么呢？？？