open, broaden, apportion
攤 centers on spreading something out: opening it up, broadening its reach, or dividing it into shares.
攤 combines 扌 (hand) with 難, which likely contributes the sound and the idea of spreading or distributing by hand.
The hand radical 扌 beside 難 suggests a hand spreading something difficult apart: opening it up, broadening it, or apportioning it piece by piece.
For タン, imagine a hand spreading tan-colored sand evenly across a beach: tan -> タン, and the hand opens and broadens the spread.