C3 exponential functions

part (c)
I frequently trip up on these type of functions, where the ln is multiplied by a constant and a variable.

So I have;
50 = 25 + 60^(-kt)
e^(-kt) = 5/12
e^[(-t/15)ln(20/11)] = 5/12

I can't figure out how to solve for t, using the power rule for the log doesn't seem to help.

Sorry about my previous post if you saw it.

How far did you get with the power rule?

Just brought -1/15 up as a power; I didn't know what to do after.

When you have exp(a*lnx) you can't quite use that exp(lnx) = x. But since you've moved the a term here, what can you do?