-- replace "undefined" by your definition
milesToKilometers m = undefined

volume r = undefined 

average x y = undefined

{- Write your answer to Exercise 2.4 in this comment:

-}

averageVolume r1 r2 = undefined


-- the following tests can be used by you, once you have implemented your functions,
-- for testing, just invoke test1, test2, ... in ghci

test1 = "test1: expected ~ 107.826048, computed: " ++ show (milesToKilometers 67 :: Double)
test2 = "test2: expected ~ 179.59438, computed: " ++ show (volume 3.5 :: Double)
test3 = "test3: expected ~ 2.070796, computed: " ++ show (average pi 1 :: Double)
test4 = "test4: expected ~ 150.796448, computed: " ++ show (averageVolume 2 4 :: Double)