I am trying to solve this equation and find x

The equation is:

e^(-2x)-7e^(-x)=8

I tried multiplying everything by e^(x), but that didnt seem to help

I got e^(x)-7=8e^(x)

That can be simplified as -7 = 7e^(x)

at this point there is not value for x that would work.

Help??

Thanks once again.