The answer would be .4% of the 150 would be boys choosing this. Here's my work.
First, I found out what 3/5 of 150 would be (divided by 5, then multiplied by 3)
Then I subtracted that number from 150 and ended up with 60 (since 3/5 of 150 is 90)
And finally, I took 60 and divided that by 150 to get .4% of the 150 students who said their fav flavor of ice cream was chocolate was boys.