模考时候出现的一道数学题，硬是做不出来。求救！！

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 of 100 units of Country R’s currency and 1percent of one’s annual income.Which of the following represents the simplified formula for the income tax, in Country R’s currency, for a person in that country whose annual income is I?

A.50+I/200

B 50+3I/100

C, 50+I/40

D.100+I/50

E.100+3I/100

正确答案选C，，求思路！

R= 2%I + (100+1%I)/2

= 50 + 2.5%I = 50 + I/40

the average of 100 units of Country R’s currency

啥意思？

应该把and 后的结合来看。是100 units of 。。。和 1% I 的平均值。