At the begging of year 1, Gulf Oil Refinery (GOR) own i0 barrels of crude oil reserve. During year t (t=1,2,.,10), the following events occur in the order listed: (1) GOR extracts and refines x barrels of oil reserves and incurs a cost c(x), (2) GOR sells year ts extracted and refined oil at a price of pt dollars per barrel; and (3) Exploration for new reserves results in a discovery of bt barrels of new reserves. GOR wants to maximize sales revenues less costs over the next 10 years. Formulate a dynamic programming recursion that will help GOR accomplish its goal?