Jamal has a flexible summer job. He can work every day but is allowed to take a day off anytime he wants. His friend Don suggests they go to the amusement park on Tuesday. The admission charge for the park is $15 per person, and it will cost them $5 each for gasoline and parking. Jamal loves amusement parks and a day at the park is worth $45 to him. However, Jamal also enjoys his job so much that he would actually be willing to pay $10 per day to do it. If Jamal earns $10 if he works, should he go to the amusement park? If Jamal earns $15 . . . ? If Jamal earns $ 20 . . . ?