The answer is the last one!
Explanation:
M represent the number of minutes. The equation shows the .15m . Meaning that they charge .15 cents every minute PLUS a flat fee of $35. The second part of the equation is the same; they charged .25 cents every m ( .25m) PLUS a flat fee of $20. All of this was shown in the last question if you look closely.
c has to be higher than 3 because none of the other numbers are equal to each other