Marcos purchases a top-up card for his pre-paid cell phone. His remaining balance, B, can be modeled by the equation B 45 – 0.05n, where n is the number of minutes he's talked since purchasing the card. a) How much money was on the card when he purchased it? b) How many minutes will he have talked when he runs out of money? this? c) What is the slope of this equation? What are the units on the slope?