So the number of outcomes with exactly 4 tails is 720/2/24 = 15. Finally we can now calculate the probability of getting exactly 4 tails in 6 coin tosses as 15/64 = 0.234 to 3 decimal places
your question doesn't make sense if an electrician came to your house it would cost $40 then $55 dollars per hour but there is no way that you can solve that (40+(55•2)=150+55=205 which is already over $190 dollars
