Dear Sapna,
as per the data you have given, it is clear that the basic salary is 65% of the Gross salary and the no. of days present is 12 out of 31 days.
hence the gross salary will be = 9000*12/31 = 3486.87 or rounded to 3484
and basic can be calculated as = 3484*65% = 2264.6 or rounded to 2265
or = 5850*12/31 = 2264.51 rounded to 2265.
pf is calculated on the basic, hence = 2265*12% = 271.8 rounded to 272
or = (5850*12/31)*12%
or = (9000*12/31)*65%*12%
any of the relations can be used as they will lead to same result and are logically correct also. it is like getting a product of 12 by either multiplting 3*4, or 2*6, or 1*12, or 2*2*3. in all cases you will get the result 12.
I hope that it is clear now.