you can take KMB bus No.278K and change MTR
Here is the information:
Get On Point:聯和墟總站
Interchange Point:粉嶺鐵路站
and then take MTR East Rail line from Fanling to Kowloon Tong.Now,change Kwi=ung Tong line from Kowloon Tong to Mong Kok.After that,change Tsuen Wan line from Mong Kok to Admiralty.Finally,change Island line from Admiralty to Fortress Hill Station
Fee:$3.2+$18.1/$8.9=$21.3(for Octopus)
$3.2+$20/$9.5=$23.2(for single ride tickets)
Times:18+60=78 mins(not included the waiting times and walking times)
KMBbus No.278K information:
http://www.kmb.hk/chinese.php?page=search&prog=route_no.php&route_no=278k
Hope above information can help you!