The correct answer is: $\frac{{{\text{Shear force}}}}{{{\text{Lever arm}} \times {\text{Width}}}}$.
The shear stress (q) in concrete of a reinforced cement concrete beam is given by the following equation:
$$q = \frac{{\text{Shear force}}}{{\text{Lever arm}} \times {\text{Width}}}$$
The shear force (V) is the force that acts parallel to the cross-section of the beam. The lever arm (d) is the distance from the neutral axis to the extreme fiber of the beam. The width (b) is the width of the beam.
The shear stress is the maximum at the neutral axis of the beam. The shear stress decreases from the neutral axis to the extreme fibers of the beam.
The shear stress is an important factor in the design of reinforced concrete beams. The shear stress must be kept below the allowable shear stress in order to prevent failure of the beam.