Velocity distribution in a boundary layer is given by u / u_∞ = sin((π/2)(y/δ)), where u is the velocity at vertical coordinate y, u_∞ is the free stream velocity and δ is the boundary layer thickness. The values of u_∞ and δ are 0.3 m/s and 1.0 m, respectively. The velocity gradient (∂u/∂y) (in s^-1, round off to two decimal places) at y = 0, is _______.