Guys and Gals,

I'm going over my old textbooks in preparation for going back to university, and one question has me totally stumped.

I understand when encountering problems like that you substitute for the exponential e.g. and solve from there, but i've now been presented with:

Can anyone advise me how I go about solving this? I'll no doubt kick myself when I see it, but I just can't figure out what to do!