Question 40642
Let the original grid size = n
No of charcters = (n*n)+24
If one row & one colmn are increased grid size = n+1
No of Characters  = (n+1)*(n+1)- 25

equating n^2+24 = ((n+1)^2)-25
we find
n^2+24 = n^2+2n+1-25
24+25 = 2n+1
49-1 = 2n
24 = n

No of characters = n^2+24 = 576+24 = 600
cheers