Question has asked for “Number of Naya mixer grinders disposed off by the end of $2000$” or cumulative sum of all the disposed Naya products by the end of $2000$. It is also known that $20\%$ of the product bought is disposed off $2$ years later.
As Naya mixer grinders were introduced in $1997$, so first disposal should be in the year $1999$ and second disposal in $2000.$
In $1999:- 20\%$ of products bought in $1997$ is disposed or $20\%$ of $30 =6 \text{(D1)}$
In $2000:- 20\%$ of the new products bought in $1998$ is disposed, or $20\%$ of $(80-30)=10 \text{(D2)}$
Total disposal $ = \text{D1+D2}=16$
Option $ : \text{B}$