ables 18. Minimizing the Cost of a Container. A trash com- pany is designing an open-top, rectangular con- tainer that will have a volume of 320 fts. The cost of making the bottom of the container is $5 per square foot, and the cost of the sides is $4 per square foot. Find the dimensions of the container that will minimize total cost. (Hint: Make a substi tution using the formula for volume.) 19. Temperature. A flat metal plate is located on a coor- dinate plane. The temperature of the plate, in de- grees Fahrenheit, at point (x, y) is given by T( x, y) = x2+ 2y2 - 8x + 4y. Find the minimum temperature and where it occurs. Is there a maximum temperature? 20. Temperature. A flat metal plate is located on a