ASK A QUESTION 'cuantas unidades hay en el libro?
I want to ask how many units the book has 'CUANTAS UNIDADES TIENE EL LIBRO?' o 'cuantas unidades hay en el libro?'(how many units there are in the book) which one is right?
Personally I would use tiene although I guess technically hay isn't wrong - just remember that for interrogatives you need to use an accent - ¿cuántas unidades?