help with integrated first order rate?

Question

Question: Reaction constant is 2.587e-3 s-1. What percent of CH3CH2CL would remain after a reaction time of 121.399s?

CH3CH2CL(g)<->CH2CH2(g) + HCl(g)

Answer 1

C=Co*e^(-kt) =>

C/Co =e^-(kt)= e^(-121.399*2.587*10^-3) =0.73 =73%