Step 1: Opportunity cost is the value of the next best alternative given up when a choice is made. Step 2: If someone takes paid employment, they give up the time they could have spent on self-employment, on leisure, or on continuing their education, so options 1, 2 and 3 are all opportunity costs. Step 3: Transportation costs to commute to work are a direct out-of-pocket expense caused by taking the job, not a foregone alternative, so this is an explicit cost, not an opportunity cost. The answer is option 4.