Answer:
Option 2 (y = 0.50 + 0.02x / y = 0.25 + 0.03x) is correct.
Explanation:
The values 0.50 and 0.25 should not change because it is a one-time fee, so option 1 and option 4 are wrong. Furthermore, the values 0.02 and 0.03 change each minute and should be multiplied with a variable. Those values must add together to get the final value. Therefore, option 3 is wrong, and option 2 is right.