Answer:
500 lb
Explanation:
You have to make a proportion:

77 lb is part of the whole weight ( which we don't know) so 77 will go on top
The problem tells us that 15.4% of the total weight is pecans so 15.4 will go over 100 (since % are out of 100)

Then you cross multiply giving you: 7700 = 15.4x
then you divide 15.4 to both sides to isolate x which will give you 500