问题如下：
Here is some information about the change of a stock price. There is 38% probability that the market will rise, 46% probability that the market will unchange, and 16% probability that the market will decline. What is the probability that the stock price equals to $45?
选项：
A.38.25%.
B.56.54%.
C.48.79%.
解释：
B is correct.
Using the total probability rule, the probability that the stock price equals to $45 is 0.38*0.65+0.46*0.56+0.16*0.38=56.54%
老师可以列一下过程吗？只知道先算三种情况的prob: 25*0.05+45*0.65+60*0.3 ; 25*0.35+45*0.56+60*0.09 ;25*0.62+45*0.38+60*0 ；然后要怎么做？
