Variable Dearness Allowance will be a fixed amount payable PER increase in the consumer price index OVER a CERTAIN POINT. In AP it is Rs 6.40 (I think it is Rs 6.40 and not Rs 6.5) per increase in the CPI over 525 points. As such when the CPI is 1225 then you have 700 points above 525 point, ie, 1225-525=700. For each point of increase over 525 points, you have to give Rs 6.4 or 6.5, as the case may be, as VDA and in this case it will be 700 X 6.4 or Rs 4480.
The above calculation is based on CPI of April, 2017. You can change according to the changes in CPI