Answers:

(i) 

If (r + 1)th term in the given expression is independent of x.

T_r+1 = ⁿC_r x^n-r a^r

For this term to be independent of x,

18 – 3r = 0

3r = 18

r = 18/3

r = 6

The term is 7^th term.

T₇ = T₆₊₁

= ⁹C₆ × (3^9-12)/(2^9-6)

= (9×8×7)/(3×2) × 3^-3 × 2^-3

= 7/18

Term independent of x is 7/18.

(ii) 

If (r + 1)th term in the given expression is independent of x.

T_r+1 = ⁿC_r x^n-r a^r

For this term to be independent of x,

9 – 3r = 0

3r = 9

r = 9/3

r = 3

The term is 4^th term.

T₄ = T₃₊₁

= ⁹C₃ × (2⁶)/(3³)

= ⁹C₃ × 64/27

Term independent of x is ⁹C₃ × 64/27.