Question: Consider the extraction of oil from a well. Let x(t) be the rate of extraction in barrels per day and p(t) the price in dollars per barrel at time t. Then R(t) = p(t)x(t) is the revenue in dollars per day. Find an expression for R(t), and give it an economic interpretation in the case when p(t) and x(t) are both increasing. (Hint: R(t) increases for two reasons)