solve for t

13e^(.081t)=25e^(.032t)

e^(.081 t) / e^.032 t = 25/18

to divide subtract exponents a^b/a^c = a^(b-c)
so
e^.049 t = 1.389
ln e^a = a in general so
.049 t = ln 1.389
You can take it from there I think.