[填空题]
The Singapore Flyer is a giant observat0g,3cxfu1mrr ion wheel in Singapore with diamet)h ,ahra6wfhv/jc:ppp8 q +- eer of 150 metres. The wheel rotates at a constant speed an) a pe:hpw, h8qj -pfh/c+v6rad completes one rotation in 32 minutes. The bottom of the wheel is d metres above the ground.
A seat starts at the bottom of the wheel.
1. After 16 minutes, the seat is 165 metres above the ground. Find d .
After t minutes, the height of the seat above the ground is given by
$h(t)=90+a \cos \left(\frac{\pi}{16} t\right), \text { for } 0 \leq t \leq 64 $.
2. Find the value of a .
3. Find when the seat is 60 metres above the ground for the third time. min
