The cell phone plan from Company C costs $10 per month, plus $15 per gigabyte for data used. The plan from Company D costs $80 per month, with unlimited data. Rule: C gives the monthly cost, in dollars, of using g gigabytes of data on Company C’s plan.

Rule: D gives the monthly cost, in dollars, of using g gigabytes of data on Company D’s plan.

a) Represent the monthly cost of each plan with an equation

b) Write a sentence describing the meaning of the statement C (2) = 40.