For this case we have to:
If there are 26 students in each grade level class and we have three classes of this type, we multiply to know the number of students:
![3 * 26 = 78](https://img.qammunity.org/2020/formulas/mathematics/middle-school/i816h8kucmhwlqxyaw451lklgfzuvfo43o.png)
Now, if there is an assembly for third grade students, knowing that 4 students were missing, we subtract to know the number of students present:
![78-4 = 74](https://img.qammunity.org/2020/formulas/mathematics/middle-school/u03gj9drjagsvatxqk2rjok74ysbjv63qt.png)
Thus, 74 students will be present at the assembly.
Answer:
74