please help with this question:

Consider an economic agent with the following production possibilities when answering the following questions. Number of Guns 0 4 7 9 11 12 Pounds of Butter 15 14 12 9 5 0 (a) What is the opportunity cost of increasing gun production from 7 to 9 guns? [2 points] (b) What is the opportunity cost of increasing gun production from 9 to 11 guns? [2 points] (c) What happens to the opportunity cost of butter as more guns are produced? [2 points] (d) Why do we assume the opportunity costs in this example are not constant? [4 points]