1. A seagull sits on the surface of the sea and moves up and down as waves pass.

Its height, $h$ metres, above its position in calm water is modelled by the function $h=\frac{3}{5}sin(90t)^{\circ}$ where $t$ is the time in seconds after timing commences.

Find the amount of time the seagull is more than 0.5 metres above its calm water position in the first 20 seconds after timing commences.

Give your answer correct to 3 significant figures.