Now if A is first order and B is also first order, then this will be our rate law. So the rate of the reaction v is equal to k, that rate constant multiplied by the concentration of A to the power of one and the concentration of B to the power of one. And the overall order of this reaction is one plus one. So we simply sum up the exponents and that gives us two. And what that means is by doubling A we double v as long as everything else remains constant. Likewise, if we double B while A and K is constant, v will also double.