It costs Marie $25 overhead and then an additional $1.25 to make each barrette. She charges $3.50 for each one. Write a function to model Marie's profit?

Given is the Overhead charges = 25 dollars.
Making charge of each barrette = 1.25 dollars.
Let's assume the number of barrette that she makes = x
So the Cost function would be, C(x) = 1.25x + 25.
She sell each piece for 3.50 dollars.
So the Revenue function would be, R(x) = 3.50x
We know the Profit function is given by the difference of Revenue function and Cost function.
Profit function = Revenue function - Cost function
P(x) = R(x) - C(x)
P(x) = 3.50x - (1.25x + 25)
P(x) = 3.50x - 1.25x - 25
P(x) = 2.25x - 25
Hence, Marie's Profit would be P(x) = 2.25x - 25.