If they sold 10 hammers and each hammer sells together with a package of nails for $12, that would be $120 total. Now subtract that from $950.50 and you get $830.50. Divide that by the remaining packages of nails sold (110 because you already sold 10 together with the hammers) and you get $7.55. Each package of nails sold for $7.55. Hope that helps!
