for eg:
Invoice value EUR 408.00
Exchange rate: 4.5
invoice value in QAR = 408*4.5 = 1836
+
freight charges QAR = 150/-
subtotal : 1836+150 = 1986

1% insurance on subtotal: 1986*1% = 19.86
Add the subtotal with insurance then you get the CIF value. i.e. 1986+19.86 = 2005.86
Now on this CIF value(2005.86) take 5% customs duty.
You will get the actual duty value.
Hope so this clarifies ur doubt.