1. A store sells two types of toys, A and B. The store owner pays $10 and $5 for each one unit of toy A and B respectively. One unit of toys A yields a profit of $2 while a unit of toys B yields a profit of $3. The store owner estimates that no more than 1000 toys will be sold every month and he does not plan to invest more than $7, 500 in inventory of these toys. How many units of each type of toys should be stocked in order to maximize his monthly total profit?