Answer:
D. All of the above.
Explanation:
We can model his budget constraint by the following first order function.
2F + 100S = 500
In which F is the number of food items that he buys and S is the number of shelters that he pays.
So A. is correct.
If we want to write this equation with F as a function of S, it is also possible:
2F + 100S = 500
2F = 500 - 100S
F = 250 - 50s
So B. is also correct
Writing with S as function of F
2F + 100S = 500
100S = 500 - 2F
S = 5 - 0.02F
So C. is also correct
The correct answer is:
D. All of the above.