Final answer:
The unit rate of game credits per dollar is calculated by dividing the total credits by the total dollars spent, which results in 4 credits per dollar.
Step-by-step explanation:
To find the unit rate of game credits per dollar, you divide the total number of credits by the total amount of money spent. In this case, you have 80 game credits for $20.
The unit rate calculation is as follows:
Unit Rate = Total Credits ÷ Total Dollars = 80 credits ÷ $20 = 4 credits per dollar.
Therefore, the correct answer is C. 4 credits per dollar.