Alright, Lets get started.
selling price = cost + markup * cost
The given selling price = $ 600
markup percent on cost = 35 %
600 = cost + 35% cost
600 = cost + 0.35 cost
600 = 1.35 cost
Dividing 1.35 on both sides
600/1.35 = cost
cost = 444.44 $
Hence the actual cost = 444.44 $ : Answer
Hope it will help :)