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 ..