Velocity of wave through the oil medium, C = Sqrt (M_b/Sigma)
Where, M_b = Bulk modulus of oil; Sigma = Density of oil
Therefore,
C Sqrt [(1.3*10^9)/(890)] = 1208.58 m/s
Now,
C = d/t, where d = distance = length of pipe; t = time taken.
Therefore,
t = d/C = 20/1208.58 = 0.017 seconds = 0.017*1000 = 17 milliseconds.