A Cargo Airline Company in South America Ferries Materials from Four

Essay

A cargo airline company in South America ferries materials from four different airfields in Brazil (called A, B, C, and D) to two different airfields in Peru (numbered 1 and 2). Distances in hundreds of miles between the six different airfields are as shown below:
$\begin{array}{ccccr}&&\text { Brazil }\\\text { Peru } & \text { A } & \text { B } & \text { C } & \text { D }\\1 & 2 & 6 & 17 & 5 \\2 & 12 & 8 & 12 & 9 \\\text { Capacities } & 60 & 40 & 75 & 55\end{array}$
Requirements for airfield 1 are 140 tons per year and 80 tons per year for airfield 2. The president of the airlines wants to determine how much material should be shipped from each airfield in Brazil to each airfield in Peru so as to minimize total travel distance.
a. How many decision variables are there in this problem?
b. What is the constraint corresponding to airfield 1?
c. What is the constraint corresponding to airfield B?