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Find the number of rows

Q.)A group of 630 children is arranged in rows for a group photograph session. Each row contains three fewer children than the row in front of it. What number of rows is not possible?
(I)3 (ii)4 (iii)5 (iv)6 (v)7
Let the number of students in the front row be x.
And no of rows=n.
Hence, the no of students in the next rows would be
(x-3), (x-6), (x-9), ………….and so on.
If n , i.e., no of rows be 3, then number of students
=x + (x-3) +(x-6) =630

=>3x = 639 =>x=213
Likewise if n=4
x + (x-3) +(x-6) +(x-9) =630
Likewise if n=5
x + (x-3) +(x-6) +(x-9) +(x-12)=630
If n=6, then
6x = 675
So, n=6 is not possible.

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