To solve the problem, we will define a function that given the weight of the package, will determine the cost of the mailing. Let x be the weigth of the package in oz and let f(x) be the cost of mailing the package. We are told that if the weight is less than 4, then the rate is 1.50. So, in math notation that would be f(x) = 1.50 if x<4. Now, we are told that if the package weights between 4 and less than 8, then the rate is 2.50. So, that is f(x) = 2.50 if 4<=x<8. Finally, we are told that if the package weights between 8 and 12, the cost is 3.50. So f(x) = 3.50 if 8<=x<=12. So the final math expression for f(x) is
1.50 if x<4
f(x) = 2.50 if 4<=x<8
3.50 if 8<=x<=12.