[求助]CFA LI 2009 June V3 教材例题疑问

哪位高手可以把　CFA LI 2009 June Volume 3 page 412 solution to 2 and solution to 3　解释的详细一些．我的疑问主要是federal statutory tax rate降低为什么会导致net deferred assets less valuable？以及　reductions in the valuation allowance could reduce reported imcome taxes(actual tax imcome taxes would not be affected by a valuation allowance established for financial reporting)in future years.

可能提问比较菜鸟级，请高手不要见笑，先谢了！