Basmati rice costs $(a−b) per kilogram in standard 7 kilogram packages, where a>b>0, and $(a) per kilogram in non-standard packages. In terms of a and b, what is the lowest possible price of exactly 24 kilograms of Basmati rice, in dollars?  Choose the correct choice from the following options:
A) 24a−3b  B) 21a−3b  C) 24a−21b  D) 21a−21b  E) 21a−24b
$(a-b) per kg in standard 7kg packs and $a per kg in non std packs.   For 24 kg we can use 3 packs of 7 kg and 3 non std packs of 1 kg each.   Leading to 3*7*(a-b)+3a= 21a- 21b+3a=   24a-21b.   ANSWER:24a−21b
<result>C</result>
Basmati rice costs $(a−b) per kilogram in standard 7 kilogram packages, where a>b>0, and $(a) per kilogram in non-standard packages. In terms of a and b, what is the lowest possible price of exactly 24 kilograms of Basmati rice, in dollars?