Clive has a phone plan where he pays double his base per minute rate for any additional minute spent on a call over twenty minutes. Part A: Determine and define the variables needed to model the situation.

Part B: Write an equation to model the situation, using the variables defined in Part A.

Part C: If Clive was charged $3.92 for a 38-minute call, what is Clive's per minute base rate? Show all work.