$$8640$$有多少个因数？  whole-number ~整数；$$factor$$ ~因数．  它的因数有$$\left( 6+1 \right)\times \left( 3+1 \right)\times \left( 1+1 \right)=56$$． 
\textbf{(2017 Math League, Priamry 6, Question \#20)}  How many whole-number factors does $$8640$$ have？  $$8640$$有多少个因数？ 

a: $$10$$ 
b: $$18$$ 
c: $$38$$ 
d: $$56$$ 