Note: A maximum number of 4 points are available for this question. Part A is worth 1 point. Part B is worth 1 point. Part C is worth 2 points. Brian received 45 trading cards from his mother and 25 trading cards from his uncle to start a collection.

Each week, Brian uses his allowance to buy a new pack of 15 trading cards to add to his collection.

The number of cards in Brian's collection can be represented by a linear function. Identify the rate of change and initial value of this function. Explain what these values represent in terms of the situation.