TPAR qn

hi sir, i am doing this question from kaplan exam kit specimen exam applicable from september 2016 and the question is:- A company manufactures a product which requires four hours per unit of machine time. Machine time is a bottleneck resource as there are only ten machines which are available for 12 hours per day, five days per week. The product has a selling price of $130 per unit, direct material costs of $50 per unit, labour costs of $40 per unit and factory overhead costs of $20 per unit. These costs are based on weekly production and sales of 150 units. What is the throughput accounting ratio? A 1·33 B 2·00 C 0·75 D 0·31 the way i have done this question is as follows:- TPAR= throughput/ limiting factor _____________________ cost/ factory hour =$20 (w1) _____ 5 (w2) =4 (w1) throughput/ limiting factor= throughput/ unit ________________ limiting factor/unit = 130-50 =80 _________ ____ =20 4 hours 4 (w2) cost/ factory hour= total factory cost ______________ total factory hour = $40 + $20 = $60 ___________ _______ =5 12 hours 12 hours i dont know where i went wrong please kindly guide me ..