It would be "llegaron". A really helpful tool is to look at some online tables that share regular conjugations for the preterite tense. Hope this helps!
Cuando es tu cumpleanos means when is your birthday.
You would answer back:
Mi cumpleanos es _________ (whenever your birthday is)
EXAMPLE:
Mi cumpleanos es 13 de febrero
Como puedo saber que Es buena estudiante? Sin saver que hizo ella
