To calculate the maximum amount of money you can hope to earn from your business now, we need to consider the condition where your parents will take 10% of your earnings above $600.
Let's assume the profit you make from your business with the additional $300 is P. According to the condition, if P > $600, you will have to give 10% of your earnings above $600 to your parents.
Therefore, the maximum profit you can hope to earn from your business is $600. Any profit above $600 will need to be shared with your parents.