It Is Possible to Hear an Approaching Train Before You $\approx$

It is possible to hear an approaching train before you can see it by listening to the sound wave through the track. If the elastic modulus is 2.0*1011 N/m² and the density of steel is 7.8 *103 kg/m3, approximately how many times faster is the speed of sound in the track than in air? (vair $\approx$ 340 m/s.)

A) 20
B) 5
C) 10
D) 15
E) 25