Solving a Sinusoidal Inequality

The position of a piston is modeled by the function $d(t) = 6\sin(4\pi t) + 2$, where $d(t)$ is the distance in centimeters from a reference point at time $t$ in seconds. The piston delivers power when $d(t) > 6$. For what fraction of each cycle is the piston delivering power?