plz help

I assume you want a cost function

Notice that each additional muffin after the first dozen costs 25 cents

So....the function that models this is

C = 4.50  +  .25N        where C is the total cost and N is the number of additional muffins after the first dozen

Here's a graph.....(I hope you can link to it )

https://www.desmos.com/calculator/x6ndvwgqtc