Answer :
If you make a table with a universe of 100 students you can check that 25 aree blond men, 60 - 25 = 35 are non blond men, 20 are blond women and 40 - 20 are non blond women. If you know that the studen is a male, you reduce the universe to 60 students. And the probability that the student is blond is 25 out of 60 = 25/60 = 0.4167 = 0.42. So, the answer is 0.42,