To calculate the cost of a quinella box you multiply the number of horses in the box by the number of horses in the box minus one. For example, a $2 quinella box 3, 4,5 would cost (3 * 2) = $6 and include the combinations 3- 4, 4 -3, 3-5, 5-3, 4 -5 and 5- 4.