A shear modulus converts a dimensionless strain into a stress by multiplication, so a stiffer material produces more stress for the same deformation. The modulus 12 Pa times strain 1/2 gives shear stress 6 Pa exactly for the stated toy elastic ledger; real soft tissues and gels have nonlinear response, viscoelastic history dependence, anisotropy, and calibration uncertainty.
A declared linear modulus maps exact strain to exact shear 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
Use a toy linear shear modulus
The checked modulus is 12 Pa and the strain is 1/2.