正反比例数学题，没学过不懂，请教

mdiandian

就是琢磨不明白，请帮忙讲讲相关原理，万分感谢！

第一题

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 sqare slab that is 3 meters long and 0.1 meter thick?

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.

第二题

the rate of a certain chemical reaction is directly proportional to the square of the concentration of chemical A preaent and inversely proportional to the concentration of chemical B present. if the concentration of chemical Bis increased by 100 percent,which of the following is closest to the percent change in the concentration of chemical A required to keep the reaction rate unchanged?

A.100%decrease  B.50%decrease   C.40%decrease  D.40%increase   E.50%increase