a = 3, d = 7
a13 = 3 + (13 – 1)7
= 3 + 84 = 87
Now, nth term is 84 more than the 13th term
an = 84 + a13
= 84 + 87
= 171
Now we have to find n,
an = a + (n – 1) d
171 = 3 + (n – 1) 7
7n = 175
n = 25
Hence, 25th term of the given A,.P. is 84 more than its 13th term