There are 26 times in washington high school as teachers. when all the teachers and students are seated in the 900 seat school auditorium, only 9 seats are unoccupied. how many students are at washington highschool

So, I assume that you mean 26 students times the teachers. 
You can create two equations out of this information.
s = students while t = teachers
26t = s
900 - 9 = 891 seats being occupied
s + t = 891
You can use these two equations for substitution.
s = 891 - t
26t = 891 - t
27t = 891
t = 31
So, 31 teachers. Now plug that back into an original equation.
s + (31) = 891
s = 860
860 students.

Is this from a