刚模了一套Prep，有道数学没看懂……
Before being simplified, the instructions for computing income tax in Country R were to add 2 percent of one's annual income to the average (arithmetic mean) of 100 units of Country R's currency and 1 percent of one's annual income. Which of the following represents the simplified formula for computing the income tax, in Country R's currency, for a person in that country whose annual income is I ?
答案是C, 50+I/40，怎么也不明白，拜托看懂的同志帮我解释一下题~感激ing~~ | 
