Question

the salary of a person was increased by 15% if his salary now is rupees £9,936 was his initial salary

Answer 1

New salary after increase = Rs. 9936
Let x be the Initial salary 
Initial salary + 15% of initial salary = New Salary
x+15%(x)=9936
x+(15/100)(x)=9936
x+(3/20)(x)=9936

x+3x/20=9936
(20x+3x)/20=9936
23x=9936*20
23x=198720
x=198720/23
x=8640 
Rs. 8640 was his initial salary. 

Answer 2

15/100 * 9936 = 1490.4
9936-1490.4 = 8445.6