The equation has a constant and a variable.
Since the store charges a flat $15 for the product, this is like the fixed cost which is a constant
So, the constant in our linear function (c) = 15
Next, the $2 for each pound of the product. So this part will vary depending upon the number of pounds of the product purchased.
Let us assume that "x" is the number of pounds of the product purchased. The variable in our linear function (mx) = 2x
The linear function is of the form: y = mx +c
The linear function in this case is : y =2x+15