In the given AP, the first term = a = 72

Common difference = d = 63 - 72 = - 9

To find: place of the term 0.

So, let a_n = 0

Since, we know that

a_n = a + (n - 1) × d

∴ 0 = 72 + (n - 1) × (-9)

⇒ - 72 = - 9n + 9

⇒ - 72 - 9 = - 9n

⇒ - 9n = - 81

⇒ n = 9

∴ 9^th term of the AP is - 81.