Steven's teacher sends the class an assignment to collect 60 different fruit seeds. Apples average 6 seeds, pears average 2 seeds, and grapes average 3 seeds. Steven has set aside 4 apples, 3 pears, and 9 grapes to extract their seeds. How many more seeds does he need to fulfill his assignment?
Please reason step by step, and put your final answer within \boxed{}.
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