1. Él trabaja.
2. Tú tocas el piano.
3. Sergio baila tango.
4. Nosotros tomamos agua purificada.
How I obtained the answers:
Firstly, él/ella/usted with an -ar verb, but particularly, this -ar verb, “trabajar”, will always drop the -ar with -a. Also, I quick note to you, “usted”, is the second person singular formal version of “you”. It's -a for -ar verbs, -ir and -er verbs are -e. I would also like to mention, -ir and -er verbs are -e for both él/ella as well.
Secondly, again, verbs. The verb “tocar”, for the subject “tú” is “tocas”, you are dropping the -ar and replacing it with the ending for “tú”, which is always -as for said subject.
Thirdly, when including an individuals name, you will usually add the “él/ella/usted” endings, -a, therefore, “Sergio baila tango”, because it's a male and you are speaking about them.
4. “Nosotros tocamos el agua purificada.”, you seem to confuse the endings -amos and -an, to be expected, actually. However, a simple thought of this:
-amos = Is everyone, including yourself.
-an = Is everyone, not including yourself.
Therefore, when you see a verb conjugated into -amos, think of everyone and yourself, and if the conjugation is an -an, then thinking of everyone, but not yourself as well.
I hope I explained this in simpler terms for further prevention of conjugating wrongly and have cleared all misunderstandings. ❤️
