Can someone provide step-by-step solutions to the problem? I provided the correct answer from my textbook so that you can check your answer. Thanks in advance!

17. Linear demand function. The cost of producing x units of an item is C(x) = 10x + 20. When the selling price is $20, twenty-one items are sold. However, when the price is $16, twenty-three items are sold. Assuming the demand function is linear, determine the price per unit and the number of units sold that will maximize the profit