求助！！prep上一道看不懂的数学题

Sherryxqr

before being simplified, the instruction for computing income tax in country R were to add 2 percent of one's annual income to the average of 100 units of country R's currency and 1percent of one's annual income.
which of the following represent the simplified formula for computing the income tax, in country R's currency, for a person in that country whose annual income is I?   
50+I/200
50+3I/100
50+I/40
100+I/50
100+3I/100
正确答案是第三个 ，，，看不懂啊看不懂

chensong211

纠结半天了～那个average～谢拉！

Sherryxqr

明了  ~~谢啦！！

kittenalways

这道题很坑爹的。。
是这个意思。。。add A  (2 percent of one's annual income) to B   (100

units of country R's currency and 1percent of one's annual income.)
2%R+(100+1%R)/2