Hey there! I'm happy to help!
For the imperfect tense of -ar verbs, you take off the -ar and put -aba on the end (adding an s, n, or mos on the end if needed depending on the conjugation).
For -er and -ir verbs, you pit ía on the end (adding an s, n, or mos on the end if needed depending on the conjugation).
An irregular verb is one that does not follow these rules. Let's look at our options.
Comías is from comer. We take of the -er and put ías on the end, so this is not irregular.
Escuchabas is from escuchar. We take of the -ar and put -abas on the end, so this is not irregular.
Ibas is from ir. We take of the -ir and put ías, put we have ibas, not ías. Ir is an irregular verb, so the answer is Ibas a casa de tus tías ayer.
Have a wonderful day! :D