Answer:
Martha's opportunity cost of growing cilantro over basil has decreased by 50%
Step-by-step explanation:
Last year Martha's opportunity cost of growing cilantro over basil was 20/25 = 0.8 bushels of basil per bushel of cilantro. Since her productions possibilities frontier of cilantro has doubled this year, her opportunity cost of growing cilantro over basil is 20/50 = 0.4 bushels of basil per bushel of cilantro.