I can't wrap my head around the wording of this problem. I've figuring it out for a long time without getting anywhere. Can anyone shed some light? The highlighted choice (choice 4) is the answer.
r = k A^2/B
Let the new concentartions be A' and B', then as B' is 100% more than B,
B'=2B, so if the rates befor and after are equal:
A^2/B = A'^2/B' = A'^2/(2B),
so A' = sqrt(2) A ~= 1.4 A, which is approximatly a 40% increase.