Hey flashylightsmeow.

The profit will be 10% of his expected costs, so if the expected cost is say h(X), then g(X) will be 0.1*h(X). Retry the problem by getting the profit function as a separate function of the total costs (the profit (remember the profit will be 10% of the costs so if the total cost is to be 100 million, then the profit will be 10 million).