A Reaction in Solution, a + B→P, Is Studied and Found

A reaction in solution, A + B→P, is studied and found to have the rate law:
Rate = k [A] with a rate constant of 3.5×10 ^{- 3} s ^{- 1}. If an experiment starts with a concentration of A of 0.20 M , at what time after the start of the experiment will the concentration of A be 0.020 M ?

A) 2.8×10² s
B) 2.0×10² s
C) 6.6×10² s
D) 2.0×10³ s
E) 3.5×10 ^{- 3} s