Answer:
C(x) = 25 + 2x
Step-by-step explanation:
He already has 25 cards.
He is collecting 2 cards per month. In x months, he will have collected:
2 * x = 2x cards
That means that the number of cards he will have after x months will be the sum of the cards he already has and the cards he collects per month:
She gave 4 because 9+4=13
