A baker calculates that by spending $16 on labor and materials, she can bake 10 cakes a day. By spending $24, she can bake 12 cakes. By spending $36, she can bake 14 cakes. In terms of capital and labor, the baker has _____.
A. negative marginal returns
B. decreasing marginal returns
C. increasing marginal returns
D. constant marginal returns