Answer :

[tex]\left(\frac{3}{7}x+9\right)-\left(\frac{2}{7}x-3\right)\\\\=\frac{3}{7}x+9-\frac{2}{7}x-(-3)\\\\=\frac{3}{7}x+9-\frac{2}{7}x+3\\\\=(\frac{3}{7}x-\frac{2}{7}x)+(9+3)\\\\=\frac{3-2}{7}x+12\\\\=\boxed{\frac{1}{7}x+12}[/tex]