A retail store sells three types of products, X, Y, and Z. The store's fixed costs are $60,000 per month. The variable costs per unit for product X, product Y, and product Z are $8, $10, and $12 respectively. If the selling prices per unit for product X, product Y, and product Z are $20, $25, and $30 respectively, how many units of each product must the store sell to maximize profit?