Kramer has 2 tests tomorrow (Econ and Nutrition) and has exactly 4 hours to study. His grade possibilities curve is based on the following:

Kramer has 2 tests tomorrow (Econ and Nutrition) and has exactly 4 hours to study. His grade possibilities curve is based on the following: 

a. In terms of grades, what is the opportunity cost of improving Kramer's Econ grade from an F to a D?

b. In terms of grades, what is the opportunity cost of improving his Nutrition grade from a D to a C?