Valeria has answer "Tengo 16 anos", So Juan asked her about her age.
"Tengo" is a from of "Verbo TENER": (Yo) Tengo, (Tu) Tienes, (El/Ella) Tiene. Since this is a direct dialogue, We should use "Tu Tienes".
So, the correct answer is: ¿Cuántos años tienes?
Hope this Helps! :)
To conjugate them, you drop the -ir ending, like you would with a regular verb like finir. Then you add, well, the regular -er verb endings: -e, -es, -e, -ons, -ez, and -ent!
Pepita es de México. es Mexicana
