One works 37.5 - although quite a lot more this month as is a particularly busy month at their work, but will get it back in lieu hours.
One - it will depend what shift they are on - they work 9.5 (ish) hour shifts for 6 days then in theory have 4 days off, but in practice, do a lot of overtime and sometimes work a double (so 18 hours). So difficult to say in a 'per week' count.
One - still a student, so depends if you mean in term time (usually about 20) or in holiday time (quite a lot more, but will take whatever is there on a zero hours so varies week to week).
Can you tell us why you are specifically asking about those in their 20s @thelionkim ?