To say “I used to go to school everyday” what form of the verb ir should you use?

Fill the blank with a la, a las, a los, or al. mi padre .

The teacher didn't explain this at all and i don't understand this

Juan: ? hola, valeria! feliz cumplea? os. valeria: muchas gracias, juan. juan: valeria: tengo 16 a? os. a. ? qué a? os tenemos? b. ? cuántos a? os tengo? c. ? cuántos a? os tienes? d. ? cuántos a? os tienen?