Momentum is generally defined as mass in motion. Therefore, every mass in motion has momentum. Momentum is related to mass and motion. As the mass and/or speed increases, momentum increases. Additionally, momentum is a vector quantity and depends on the direction of motion.
Mathematically;
Momentum = mass*velocity
In the current case:
m1 = m2 = 30 kg
v1 = 2 m/s
v2 = 4 m/s
If motion to the right is taken positive and that to the left is negative, then momentum of the two bicycles before collision is given by;
Momentum = mass(v1-v2) = 30(2-4) = -60 kg-m/s (that is, the momentum is 60 kg-m/s to the left).
