Solution:
First term = 4
a = 4
Common difference = 9 - 4
d = 5
n = 17
General term of an A.P
tn = a + (n - 1) d
tn = 4 + (17 - 1) (5)
= 4 + 16 (5)
= 4 + 80
= 84
Therefore 17th of A.P is 84