Can you tell me how many root canals needed in tooth #24?

Just one: There should be just a single canal in that tooth. In a rare instance there may be two.

Tooth #24 1-2 canals: Teeth always have at least one root, and each tooth root always has at least one root canal. But beyond that basic format the variability exists. Lower incisors (teeth #23,24,25,26) have 1 root canal and possibly 2.

Generally: Generally lower incisors have 1 root canal, bet occasionally 2. Additionally there may be tiny accessory canals at the apex, the end of the root, making it look like the Nile River Delta. An Endodontist, a root canal specialist, is the Dentist best trained and experienced to address Root Canal Disease.