"given that it's a senior" is an important piece of info that tells us to only focus on the "seniors" column. The word "given" is an indication that we know this information 100%
There are 5 seniors (2+3 = 5) and 2 of them are male. So 2/5 = 0.40 = 40% of the seniors are male. The probability of selecting a male, if we know this person is a senior, is 40%
