3,000 RMB = 3,657.9 Hong Kong dollars
The bank exchange rate of 0.8 1 you mentioned refers to the exchange rate of converting Hong Kong dollars into RMB, that is, 1 Justin Hong Kong dollars equals 0.8 1 RMB.
Therefore, the correct exchange of 3,000 RMB for Hong Kong dollars should be 3,657.9 Hong Kong dollars.