Choose the correct equivalent factored form for the expression below.
x^4 - 121

There are 16 students total.
1/4 (4 students)--> Yellow Costumes
6 students--> Purple Costumes
(?) students--> Orange Costumes.

We know that one fourth of the students is 4 students by doing simple division.
6 students are wearing purple costumes. 
Add these together.
4+6 = 10

The remaining students are wearing orange costumes.
There are 6 students remaining.
Therefore, 6 students are wearing orange costumes.

6 Students