In the post-apocalyptic wasteland, 1 lizard is worth 8 bottle caps, 3 lizards are worth 5 gallons of water, and 1 horse is worth 80 gallons of water. Marla can scavenge for 20 bottle caps each day, but needs to pay 4 bottle caps per night for food and shelter. How many days does it take Marla to collect all the bottlecaps she needs to buy a horse?