How to solve this question? :)

I think it's 20 i don't know man

answer:   78125

step-by-step explanation:

since, the total number of seats = 25

and, there are 5 rows of 5 seats.

number of students in first grade = 15

number of students in second grade = 5

also, all the first-grade students occupy the first 3 rows,

thus, in first row total number of possible arrangement = 15

in second row total number of possible arrangement = 15

in third row total number of possible arrangement = 15

in fourth row total number of possible arrangement = 5 ( because all the first grade students got their seats )

in fifth row total number of possible arrangement = 5

thus, the total number of possible arrangement of sitting in 25 seats = 15 × 15 × 15 × 5 × 5 = 3125 × 25 = 78125