We are asked to figure out the best estimate of the total number of pecans sold last year and this year.
Recall that the best estimate is not the exact number but rather an estimate that is closer to the exact number.
Let us round off the number of pecans sold last year and this year to the nearest 1 billion places.
Finally, add the numbers
Therefore, the best estimate of the total number of pecans sold last year and this year is 10,000,000,000 (Option D)