I see this as a basic equation.
If she starts at point x, 8 feet, then goes down another 13, she is adding to the number of feet she traveled down.
So your answer would be 8+13=21
If this isn't what you needed, because I am not sure what math you are taking, let me know if I can help you more!
1/2 probability of 1 flip
1/2 x 1/2 x 1/2 x 1/2 = 1/16 probability
For this, all you need to do is subtract 2m on both sides, and your answer will be: -1 = m
Brooke needs to get a 98 on the final to get an average of 80.
So you know that the total of the five given score is 382 by adding all the scores.
Now you multiply the average, 80 by 6 for the total of six tests including the final which is 480
Then you subtract 480-382 to find your answer.