OG 11 - PS & DS

請問大家有興趣研究OG 11 - PS & DS的問題嗎?

我實在解不了一些題目.

#170

In a certian Co., the ratio of the no. of managers to the no. of production-line workers is 5 to 72. If 8 additional production-line workers were to be hired, the ratio of the no. of managers to the no. of production-line workers would be 5 to 74. How many managers does the co. have
A)5
B)10
C)15
D)20
E)25

近似的ratio,總是算不了.Need Help