In an article, the maximum shear stress τ of a cracked concrete member is given to be τ = τ0(1 − kw), where τ0 is the maximum shear stress for a crack width of zero, w is the crack width in mm, and k is a constant estimated from experimental data. Assume k = 0.28 ± 0.04 mm−1. Given that τ0 = 50 MPa and w = 1.0 mm, both with negligible uncertainty, estimate τ and find the uncertainty in the estimate.