You use many after 'how' to ask questions about numbers or quantities. You use many after 'how' in reported clauses to talk about numbers or quantities.
1. a quantifier that can be used with count nouns and is often preceded by `as' or `too' or `so' or `that'; amounting to a large but indefinite number;
"many temptations""the temptations are many""a good many""a great many""many directions""take as many apples as you like""too many clouds to see""never saw so many people"