solve exponential

edit

I've just started to experiment with Sage, so I might be missing something simple here. What I'm trying to do is to solve the following equation:

var('t','k1','k2','y1','y2')
assume(k1>0,k2>0,y1>0,y2>0)
assume(k1,'real')
assume(k2,'real')
assume(y1,'real')
assume(y2,'real')
assume(t,'real')
solve(y1*exp(-t/k1)/k1 - y2*exp(-t/k2)/k2==0,t)

The result is[e^(t/k2) == k1*y2*e^(t/k1)/(k2*y1)], and not fully solved for some reason. I was expecting something like

t==ln(y2*k1/y1*k2)/(1/k2-1/k1)