You two are too polite. Satoshi, you do not need to say sorry if you just borrow 20cents. Relax and use a more relaxed tone. Just like what the professor taught above.

very nice. Both very polite. You can be a bit more casual to ask for 20 cents!

Can say something like, 'Hiya I am 20 cents short for the bus ride. Can I borrow it?