Bayes' theorem Reading 8 Schweser Comprehensive Prob #3 regarding, question, appears, problem

Benjiko

My question is regarding the answer that appears for this problem. The book says the answer is calclulated by: 30% / 51.25% = 58.25%.
However, according to Bayes’ theorem:
P(I|O)= [ P(O|I) / P(O) ] x P(I)
So, why don’t they later multiply the 58.25% above by the 75% that is the probabilitiy of Score >= 20?
Thanks for your help guys.