Sales = Output Sold x Price Per Unit = 800 x 20 = Rs 16000 crore.
Now, Value of Output = Sales + Change in Stock = ? [16000 +(-500)] = Rs 15500 crore .
Now, GVAMP = Value of Output - Intermediate Cost = Rs (15500 -8000) = Rs 7500 crore.
Hence, NVAMP = GVAMP - Depreciation = Rs (7500 - 1000) = Rs 6500 crore