"How many books are they taking?"
Translation:Wanachukua vitabu vingapi?
Taka (from verb "kutaka") means "to want". As in an imperative way. Plus depending on the context, it can also be translated as "to plan to do sth". See examples:
Ninataka kuona mimi mwenyewe (I want so see for myself)
Anataka kutuambia ukweli wote (He plans/wants to tell us the whole truth)