We are given function: f(x) = 15x + 4.50
That represents the total cost , f(x) , Ismael charges for pizza pies and drink.
We can see the situation that Ismael is being charged for pizza pies and drink.
For each drink the cost is fix that is $4.50.
If there are x number of pizza pies, there would be total cost of x pizza pies at the rate $15 each pizza pie is 15x.
Therefore, coefficient 15 represents the cost of each pizza pie.