In Newton's Third law of motion, the 'action' and 'reaction' forces act on different objects. That's why they don't cancel each other out and always result in zero force.
Answer:
Case A
Explanation:
given,
size of bacteria = 1 mm x 1 mm
velocity = 20 mm/s
size of the swimmer = 1.5 m x 1.5 m
velocity of swimmer = 3 m/s
Viscous force

for the bacteria


for the swimmer


from the above force calculation
In case B inertial force that represent mass is more than the inertial force in case of bacteria.
Viscous force is dominant in case of bacteria.
So, In Case A viscous force will be dominant.
direction ................................................................
1km=10^3 m,1km^3=10^9cubic metres answer is 1.4x10^18cubic meters