Assume you are planning a spring break ski trip to Colorado. You are preparing a budget of your costs. You are staying at a lodge that has a special where the lodge charges you $25 for the first 30 ski lift rides and an additional charge of $5 for each ride in excess of 30. You believe you will ride the ski lift 40 times during the week, so you budget $75. The ski lift cost is an example of a

a) step cost b) fixed cost c) variable cost d) mixed cost