Logistic: 40/(1+11e^(-.08t)) what is t when equal 20

Logistic problem: p= 40/(1+11e^(-.08t))
what is t when the population reach 20?
p=population
How would I solve this, sets please? thanks

20 = 40/(1+11e^(-.08t))
11e^(-.08t) = 1
t = - ln(1/11) /0.08
t = 29.973