For what value of n will the arithmetic series 2+9+16+... equal to 1512

Please show all working :)

a = 2
d = 7
1512 = [4+7(n-1)]*n/2
3024 = n(7n-3)
7n^2-3n-3024 = 0
complete the square
n^2-3n/7=432
(n-3/14)^2=432+9/196
n = 3/14±sqrt(432+9/196)
n=21

Both you and Mike are great!
What is n? You did not mention anything about n!!!