The problem requires an excel solution and an algebraic solution with variables: During the month of July, Pittsburgh resident Bill Fly must make four round trip flights between Pittsburgh and Chicago. The dates of the trips are shown in Table 4.75. Bill must purchase four round-trip tickets. Without a discounted fare, a round-trip ticket between Pittsburgh and Chicago costs $500. If Bill's stay in a city includes a weekend, he gets a 20% discount on the round-trip fare. If his stay in the city is at least 21 days, he receives a 35% discount If his stay is more than 10 days, he receives a 30% discount. However, at most one discount can be applied toward the purchase of any ticket. Determine how to minimize the total cost of purchasing the four round-trip tickets. (Hint: it might be beneficial to pair one half of one round trip ticket number with half of another round-trip ticket.) Table 4.75: Flights for Bill Fly Problem: Leave Pittsburgh: Leave Chicago: Monday, July 1 Friday July 5 Tuesday July 9 Thursday July 11 Monday July 15 Friday, July 19 Wednesday July 24 Thursday July 25