Are you sure about the equation? If you substitute 30 in the equation you get
(x-2)(300/x + 55) = 120
28*65= 1820 doesnтАЩt equal to 120
Also what happens to the part of the question that says тАЬthe total revenue from the sale of the calculators was $ 120 more than the cost of the shipmentтАЭ
I agree with LHS of the equation, but not sure about the RHS.