The number of radians (d) that the wheel have turned may be calculated by the equation,
d = (v1)(t) + 0.5 x a x t²
where v1 is the initial velocity, a is the acceleration, and t is time. Substituting the known values
d = (18 rad/s)(3s) + (0.5) x (-2 rad/s²) x (3s)²
The value of d is 63 radians.