Let and be the cost and weight, respectively. We are told that first-class postage was for up to Remember that
up to means
less than or equal to. In this case, the rule and domain for the first step can be written as shown below.
Since the cost increases by for each additional ounce, we can write the rule of the next steps by adding to the first step until the domain reaches to
The function we wrote pairs every number in each interval with a single value. Therefore, it is a step function. Each piece of its graph will be a horizontal line that is missing its left endpoint. We will show the left endpoints using open points and the right endpoints using closed points. Let's graph it!