I think the easiest way to think of this is to pretend that there are a total of 100 students at the high school, so that means the amount of people who work part time is 45% of 100 = 45 people. If 60% of those students love math, you do 0.6 * 45 = 27 people.
Next, 80% of the students who do not have a part time job (100 - 45 = 55) love math, so 0.8 * 55 = 44 people.
44 + 27 = 71, so the percent is 71/100 = 71%.
let me know if any part of that doesn't make sense
when you do this you subtract the annual fee of $100 from the total payment $225 which leaves you with $125 then you divide it by The fee for each class Which is $5 so you get 25 classes