i understand most of the problem but where did the 0.84 M come from?

Question

a drug was injected into your body with a 2.00 M concentration. what would be its concentration after 0.010 seconds if k = 875 ^ -1

1st order reaction!

ln [ A ]t = - (875 ^ -1) (0.010 SEC) + ln (2.00)
= - 0.1769

[ A ] t = e^ -0.1769 = 0.84M