[求助]数学题

huangxiaoyan

A certain telephone company offers two plans, A and B, under plan A, the company charges a total of $0.6 for the first 7 minutes of each call and $0.06 per minute thereafter. Under plan B, the company charges $0.08 per minute of each call. What's the duration of a call, in minutes, for which the company charges the same amount under plan A and under plan B ?

答案是9.

我算了一下，好像算不出来。

shallpoo

0.6 + 0.06 *（N-7）= 0.08 * N

huangxiaoyan

多谢