Nigel is selling candy bars for his outdoor club. He is averaging 4 bars every 3 days. If he continues at this rate, how many days will it take to sell his box of 36?

Nigel is selling candy bars at a rate of 4 bars/3 days.

To sell 36 bars at this rate, it will take him (36 bars)/(4 bars/3 days) = (36 * (3/4)) = 27 days. Answer: \boxed{27}.