The Following Reaction Is First Order in a and First

The following reaction is first order in A and first order in B: A + B → Products Rate = k[A][B]
What is the rate constant k of this reaction in vessel (b) relative to the rate constant k of this reaction in vessel (a) ? Each vessel has the same volume.Shaded spheres represent A molecules,and unshaded spheres represent B molecules.

A) rate constant k in vessel (b) /rate constant k in vessel (a) = 1:2
B) rate constant k in vessel (b) /rate constant k in vessel (a) = 1:1
C) rate constant k in vessel (b) /rate constant k in vessel (a) = 2:1
D) rate constant k in vessel (b) /rate constant k in vessel (a) = 4:1