A viscous shear stress equals viscosity times shear rate, so a thicker fluid produces more stress for the same rate. With viscosity 4 Pa*s and shear rate 2 reciprocal seconds, the stress is 4 times 2 = 8 Pa exactly for the stated toy Newtonian model; real viscoelastic flow can have non-Newtonian viscosity, temperature dependence, wall slip, instrument calibration, and measurement uncertainty.
A toy viscosity maps a checked shear rate into checked stress. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
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The viscosity is 4 Pa*s and the checked shear rate is 2 reciprocal seconds.