-- 6 --
itemTotal :: [(String, Float)] -> [(String, Float)]
itemTotal [] = []

itemTotal (x:xs)
   | elementInList (fst x) xs == True = itemTotal (sumPrices xs (fst x) (snd x))
   | otherwise = x:(itemTotal xs)


elementInList :: String -> [(String, Float)] -> Bool
elementInList _ [] = False
elementInList y (x:xs)
   | y == fst x = True
   | otherwise = elementInList y xs


sumPrices :: [(String, Float)] -> String -> Float -> [(String, Float)]
sumPrices [] _ _ = []
sumPrices (x:xs) y price
  | fst x == y = (y, snd x + price):xs
  | otherwise = x:(sumPrices xs y price)

---------------

itemDiscount :: String -> Float -> [(String, Float)] -> [(String, Float)]
itemDiscount _ _ [] = []
itemDiscount item discount (x:xs)
  | item == fst x = (item, applyDiscount (snd x) discount):(itemDiscount item discount xs)
  | otherwise = x:(itemDiscount item discount xs)


applyDiscount :: Float -> Float -> Float
applyDiscount price discount = price * ((100-discount) / 100)