Reaction kinetics- first order reaction rates?

Question

First order reaction of N2O4 to form 2 mol of NO2 has rate constant k=0.023 min-1. How long will it take the initial concentration of N2O4 to decrease to 10% of the original value?
a)600s, b) 100 min c)43.5s d)43.5 min e) 435 min

How to do this question?
THANKs

Answer 1

(1-.1)/0.023/min = 39.1 minutes

interesting - the 43.5 minutes is how long it takes ALL to be used up not 90% - so answer key has mistake

but answer d) is clearly the closest

Answer 2

I think you just look at the slow step... There are 2 NO2 So... [NO2]^2