If I understand correctly your total annual income excluding your "housing allowance" is 30000*12 + 25000*4 = 460000.
Assuming that your employer "exercises proper control" to the satisfaction of the Inland Revenue that you do actually spend the housing allowance on housing, then that allowance will be deemed to have a taxable value of 10% of the rest of your income. i.e. 10% * 460000 = 46000
Your total taxable income will therefore be 460000+46000 = 506000
From the tax calculator here:
http://www.ird.gov.hk/eng/ese/st_com..._07/stcfrm.htm
the tax you pay would be $66,640 assuming that you are single and have no dependent relatives in Hong Kong.
The effective rate on your actual cash income of 580,000 is therefore 11.49%.