If the piston is pushed at a speed of 5 mm/s, the air comes out of the nozzle with a speed of 0.1 m/s

From equation of continuity: A1V1 = A2V2
Subscript 1 stands for piston and 2 for nozzle respectively.
We have:
d1 = 20 mm
d2 = 1 mm
Therefore, A1 = π(20²) and A1 = π(1²)
Also, V1 = 5 m/s
Thus, π(20²)×5 = π(1²)×V2
V2 = 2 m/s