you can make the u with an acute accent (ú) in windows by holding down your alt key and typing 0250. (there might be an easier way, but that's the way I know!) Or you can use the little special character input integrated in duolingo. If all else fails you can use your windows character map (usually somewhere in the accessories menu). On most smartphones if you press and hold the letter it will give you a little popup menu of accented versions of that letter.
On a cellphone, hold down the 'letter' you need ie u & ú. On a pc I've only ever used the symbol tool.
Where is boleto/boleta from? I've lived in Spain for four years and never ever heard boleto/boleta, only billete or ticket.
I misspoke, sus is the "more formal-usted" version, but su or sus depends on whether you are talking about one thing or more than one. Plurality fits the object.
Usted is also correct. It would be used when speaking to someone more formally, as you would to someone who you don't know or someone to show respect.
why can ticket be both "boleto" and "boleta"? why and when is the gender change used?
I have two choices, both of which are correct. You were not specific as to familiar (tu) or formal (usted). I have both answers.
Usually if the word ends in an o, it's masculine. If it ends with an a, feminine.