The exponent of power of $x$  occurring in the $7^{th}$  term of expansion of ${\left(\frac{3x}{2}-\frac{8}{7x}\right)}^9$  is

Given expansion is${\left(\frac{3x}{2}-\frac{8}{7x}\right)}^9$  

We have general term in the expansion ${\left(x+a\right)}^n$

$(\therefore T_{r+1}={}^n{\text{C}}_r{x}^{n-r}{\left(a\right)}^r$ be the expansion of ${(x+a)}^n)$  

$7^{th}$  term of expansion

$T_7=T_{6+1}={}^9{\text{C}}_6{\left(\frac{3x}{2}\right)}^{9-6}{\left(-\frac{8}{7x}\right)}^6$

$T_7=T_{6+1}={}^9{\text{C}}_6{\left(\frac{3}{2}\right)}^3{\left(-\frac{8}{7}\right)}^6{x}^{-3}$  $\left(\therefore \frac{x^a}{x^b}=x^{a-b}\right)$  

The exponent of power of $x$  be the $-3$ (power of $x$ )