This question is asking for relative risk reduction (RRR).

First, use the table to calculate relative risk (RR).

RR = (a / (a + b)) / (c / c + d))

In this case, you can simply use 0.12 and 0.04. There is a 0.12 recurrent stroke rate for standard treatment. This is your (c / (c + d)). There is also a 0.04 recurrent stroke rate for women taking the new antiplatelet drug. This is your (a / (a + b)).

RR = 0.04 / 0.12 = 0.33

Now, calculate RRR.

RRR = 1 - RR = 1 - 0.33 = 67%

Important to not confuse the equations on this one. Because they asked for women only, we can eliminate the mens information.

RR = ET/ EC =33%

ARR = EC - ET = 8%

RRR = EC - ET / EC = 67% (our answer)