a = 3, d = 7

a₁₃ = 3 + (13 – 1)7

= 3 + 84 = 87

Now, n^th term is 84 more than the 13^th term

a_n = 84 + a₁₃

= 84 + 87

= 171

Now we have to find n,

a_n = a + (n – 1) d

171 = 3 + (n – 1) 7

7n = 175

n = 25

Hence, 25^th term of the given A,.P. is 84 more than its 13^th term