Question: A consumer has a utility function U(z, r) = z + 80r - r2 , where r stands for the number of roses and z is the number of zinnias. She has 400 square feet to allocate to roses and zinnias. Each rose takes up 4 square feet of land and each zinnia takes up 1 square foot of land. She gets the plants for free from a generous friend. If she were to expand her garden for flowers by another 100 square feet of land, she will
(a) Plant 100 more zinnias and no more roses.
(b) Plant 25 more roses and no more zinnias.
(c) Plant 96 zinnias and 1 rose.