Hi, What is the cheapest and fastest way from the airport to Silka Hotel Mongkok?

Do you refer to Silka West Kowloon Hotel at Mong Kok? If so, airport shuttle bus no. E21 can take you to Ming Kei College, Cherry Street, from where you can easily walk to your hotel within several minutes. But it takes about 75min for the whole journey and the bus fare is only 14HKD.
For the faster transport, the Airport Express Train and subway are suggested.