bus to take from HK airport to Metropark Hotel Kowloon 75 Waterloo Road

Hi, I'm afraid there is no direct bus between the two destinations.
At the airport, you can take ahuttle bus E21 and get off at Lantau Link Toll Plaza Station. There you can transfer to bus no. E21A to Man Kee Mansion, Waterloo Road. After getting off, you can walk to your hotel.
There is also easy way. You can take the airport express to reach Kowloon Station and then take the free shuttle bus to reach your hotel. It is much easier for you to find but expensive.

How long it Take E21 from airport to Man Kee Mansion

The bus takes about 90 minutes, btw, after bus E21, you need to switch to bus E21A at Lantau Link Toll Plaza and then get off at Man Kee Mansion, Waterloo Rd.