1.A rectangular field is to be enclosed on four sides with a fence. Fencing costs $ 5 per foot for two opposite sides, and $ 2 per foot for the other two sides. Find the dimensions of the field of area 760 ft^2 that would be the cheapest to enclose. 2.If the price charged for a bolt is p cents, then x thousand bolts will be sold in a certain hardware store, where p=80-x/20. How many bolts must be sold to maximize revenue? 3.Suppose c(x)= x^3 - 20x^2 + 30 000x is the cost of manufacturing x items. Find a production level that will minimize the average cost per item of making x items