import Control.Monad
import Control.Applicative
import Data.List
import Debug.Trace
import Numeric.LinearProgramming

--Uses the GNU GLPK linear programming library

spy x = trace (show x) x

main = do
 n <- readLn
 forM_ [1..n] (\n -> putStr ("Case #" ++ show n ++ ": ") >> solve)

solve = do
	[n',v',x'] <- spy . words <$> getLine
	let n :: Int ; n = read n'
	let v :: Double ; v = read v'
	let x :: Double ; x = read x'
	[rs,cs] <- transpose <$> forM [1..n] (\_ -> map read . words <$> getLine) :: IO [[Double]]
	if (all (<x) cs || all (>x) cs) then putStrLn "IMPOSSIBLE" else print $ f n v x rs cs

f n v x rs cs' =
	let hs = zipWith (*) rs cs
	    cs = map (subtract x) cs'
	    problem = Maximize rs
	    bounds = [x :<=: 1 | x <- [1..n]]
	    constraint = Dense [hs :==: 0]
	    Optimal (maxFlow,_) = spy $ simplex problem constraint bounds
	in v / maxFlow