Marisol must send fewer than 84 snack packs.
84x.25=21+4=25
Try this solution:
1. for probability of both televisions work:

2. for probability of at least on is defective (it means, the sum = one is defective and two are defective):
- for P(1defective);
- for P(2defective);
totaly for at least one is defective:

You would move five down and eight to the right, it depends how how the grid is
The side that is parallel to the side that is 15 yards, the one that is 6 yards.
subtract 6 from 15 (15 - 6) and you get?
that is your answer.
1/2 x base x height
1/2 x 6 x 8 = 24 (a)