A microfluidic constriction is checked by equal volumetric flow. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
Narrower channel carries faster flow
The upstream area is 2 square metres and the speed is 3 m/s.
Aup=2m2,vup=3m/s
Flow is area times speed on both sides
Both products give 6 cubic metres per second. The claim is continuity only, not pressure drop or viscosity.