Need some help. have the A part of the question but do not know how to set B or C.

Question

Butadiene (C4H6) reacts with itself to form a dimer with the formula C8H12. The reaction is second order in butadiene. If the rate constant at a particular temp is 0.04/(M s) and the initial concentration of butadiene is 0.02M
A. what is its molarity after a reaction time of 1.00 h?
60min x 60 sec= 3600s
1/A = 0.04M/s(3600s)+1/0.02
1/A = 144 + 50
1/A = 194
A = 1/194
=5.2x10^-3M

B. what is the time in hours when butadiene concentration reaches a value of 0.002 M?
C. What is the half life of the reaction?

Answer 1

i figured out part C as well
t1/2 = 1/K(A)
t1/2 = 1/(0.04)x(0.02)
t1/2 = 1/8x10^-4
t1/2 = 1250sec
t1/2 = 1250s/60m
half life = 20.833min

Still do not know how to set up part B. Can anybody help out?