Question

¿Cuántos espejos hay en tu casa? how to respond

Answer 1

Cuántos=How many
since it's asking you an specific amount i believe it would be better by responding in numbers
one=un
two=dos
three=tres
four=cuatros
....
You can use any of the following verb to say how many you have depending if there's one or more
Hay(verb)=there are
Tenemos(plural) we have
tengo (I have)

Since it's asking you, you will have to change "en tu" to "en mi".("in your to in my)

Give it a try now :)