Yes, that is the correct answer.

Now, how did we get that?

From this definition of Young's modulus, we can solve for the compression l,

l = [ (7 x 10⁴ N)(4 m) ] / [ (20 x 10¹⁰ Pa)(8 x 10 ^{- 3} m²) ]

l = 1.75 x 10 ^{- 4} m

(c) 2000, Doug Davis; all rights reserved.