You need to use the equation that relates the old salary and the new increased salary such that:
`9936 = s + 15/100*s => 9936 = s + 0.15s`
Factoring out s yields:
`9936 = s(1 + 0.15) => s = 9936/1.15 => s = 8640`
Hence, evaluatingthe initial salary, before being increased, yields `s = $8640` .
Let the original salary be x then the new salary is x(100+15)/100 or 1.15x
1.15 x = 9936
x = 9936/1.15 = 8640
The original salary is 8640
9936 is the increased salary and was increased by 15% means 115%. In value it is 1.15. Use this formulae Cost price x multiplier = Sale Price
Now put values.