If there are 26 students in each third-grade class and 3 third-grade classes in the school, how many students will attend an assembly for third graders if a total of 4 students are absent?

26 students in each third-grade class and 3 third-grade classes in the school
so total of 3  third-grade classes students = 3 x 26 = 78 third-grade  students

 4 students are absent then 78 - 4 = 74

answer
74 students will attend an assembly for third graders