The above is correct in terms of MoA, however I believe the stem states it is PT (prothrombin) prolongation, not PTT (Partial Thromboplastin). I did not have any idea what dicumarol was.. but here was my logic:

1. Patient had aortic valve replacement, she's 80, probably put on an anti-coagulant
2. I know Warfarin is sold under the brand name Coumadin
3. Remind yourself that Warfin was discovered in 1927 (10,9,2,7) and inhibits Vit K dependent clotting factors (vit K deficiency-like state)
4. Pronounce the drug not in FA as diCOUMarol, and you shall hopefully now know it also inhibits epoxide reductase, and pseudo guess your way to victory.

Dicumarol is a competitive inhibitor of vitamin K epoxide reductase.

Or process of elimination using knowledge of increase PTT time: something wrong with 12, 11, 9, 8.

for completion sake; Dicumarol is an epoxide-reductase inhibitor like warfarin and just like when you use warfarin the first clotting factor to go is seven since it has the shortest half-life. Factor seven is part of the extrinsic pathway and therefore will have a prolong your PT.