Answer: $2.50
Step-by-step explanation:
We all know that national defense is a non excludable and no rival good which means that one person cannot exclude others from consuming it and the consumption level of national defense remains the same for all the citizens, it will not be reduced from the consumption of one individual.
It was given that each person values every dollar that is contributed towards national defense is at %0.25.
Therefore, if Bob contributes $10 to the national defense fund then his personal valuation of the increase in the fund is only (0.25 × 10)= $2.50.