问题
单项选择题
The equation 
relates the values of two linked currencies, where R is the value in dollars of one currency and S is the value in dollars of the other currency. Which of the following equations can be used to convert dollar values from the R currency to the S currency ？（）
A.A
B.B
C.C
D.D
E.E
答案
参考答案：A
解析：
You can simplify the equation by multiplying 7 times both sides, which results in the equation 
, which can be restated as 5R-15=4S+32, which can be restated as 
.