Merchandise subject to terms $\frac{3}{10},\frac{n}{30},$ FOB shipping point, is purchased for $$10,000.$ The seller paid transportation costs of $$500$ and added it to the invoice. There was a return of $$2,000$ prior to payment. If paid within the discount period what is the amount of the cash discount allowable to the buyer?

a$.$ $$100$

b$.{?}^{****}$$$240$

c$.$ $$480$

d$.$ $$280$