Applicative and Monad instances for a function type?

Question

I have a data type that resembles Blah below but because of a quirk with the type I cannot automatically derive Functor, Applicative, and Monad. So I must do it manually, but I'm not sure how. I tried to take inspiration from the instances for ((->) a), but I can't quite figure out the Monad instance.

newtype Blah a = Blah (String -> a) -- deriving (Functor, Applicative, Monad)

-- this seems right
instance Functor Blah where
  fmap f (Blah g) = Blah (f .  g)

instance Applicative Blah where
  pure = Blah . const
  -- This is right, right?
  (<*>) (Blah f) (Blah g) = Blah $ \x -> f x (g x)

instance Monad Blah where
  return = pure

  -- I'm not having any luck here.
  (>>=) a b = Blah $ \c -> _

Edit: Someone marked this as a duplicate of another, but I don't see where I would've gotten the answer from that. The newtype wrapper is what made this difficult. I looked up the Monad instance in base for (->) a before I wrote this question, but the gymnastics in the answer here are what I needed.

Answer 1

How about

Blah f >>= g = Blah $ \s ->
    let Blah h = g $ f s in h s