Can you me ? i need to know how to find the equation and can you explain how you got it

To start, first multiply 3 and 2.50 together to find the starting price we know so far about the amount of money Roman spends. This would be $7.50. Then, since we do not know the amount of popcorn bought, or x, and we know the price of it, 4.25, we can write this as 4.25x. Then, to find the total cost, write this as y=4.25x+7.50.