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7. (10 pu) LauMac Industries finds that the marginal-profit, in dollars, from the sale of x digital control boards is given by P'(x) =260 3. A customer orders 1,000 boards and later increases the order to 1.200. Find the extra profi resulting from the Increase in order size. b. How many boards do they need to sell to achieve a profit of $13,000? C. How fast is their rate of profit changing when they sell 1, 400 boards