Answer:

Explanation:
Let be "x" the number of percussionist that are on the sidelines.
The procedure to find "x" is:
1. There are 2 percussionists on the sidelines to every 13 marching instruments, then the sum is:

2. Knowing that the high school band has 180 total members, you can write the following proportion:

3. Finally, you must solve for "x" in order to find its value:

Therefore, there are 24 percussionists on the sidelines.