Find the sum of t

The arithmetic progression is given.
Here first term is 7 and common difference is
Last term l = 84

Let no. of terms be n.
Since, a_n = a + (n - 1)d

Where,

a = First term of AP
d = Common difference of AP
and no of terms is ‘n’

⇒
⇒
⇒ 22 = n – 1
⇒ n = 23

Since the sum of n terms is
S_{n =}
So sum of 23 terms S₂₃
]
= 11.5 [14 + 22 × 3.5]
= 11.5[ 14 + 77]
= 11.5 × (91)
= 1046.5

Hence, Sum is 1046.5 = .