问一道prep数学题～

175.
                18356-!-item-!-187;#058&011490

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  50+I/40

今天做prep做到的，刚查了prep数学解释也没有～～～

不懂。。。。求教～～～