7. The product of two positive numbers is 576. The sum of the first and four times the second is minimized. Find the two numbers. a) 24 and 24 b) 36 and 16 c) 48 and 12 d) 96 and 6 e) Both numbers are 12v/3 8. An open box can be made from a square piece of material, by cutting equal squares from each corner and turning up the sides. Find the dimensions of the box of maximum volume if the material has dimension 20 cm by 20 cm. a) 10 40 40 3 cm x - cm x 3 cm b) 7.5cm x 7.5cm x 5 cm c) 4.5 cm x 4.5 cm x 11 cm d) 3.5 cm x 3.5 cm x 13 cm e) 6cm x 6cm x 8 cm 9. Find all intervals on which the function y = 623 - 24 is concave upward. a) (-0o, 0) and (3, 00) b) (-00,0) and (6,00) c) (-00,3) and (6, 00) d) (0, 3) e) (3, 6)