Answer
$\frac{5x}{4}$
Work Step by Step
By inspection, we see that the LCM of the denominators is $36$. Therefore, we create a common denominator using this LCM and obtain:
$\frac{6x}{9}+\frac{7x}{12}$
=$\frac{4(6x)+3(7x)}{36}$
=$\frac{24x+21x}{36}$
=$\frac{45x}{36}$
=$\frac{15x}{12}$
=$\frac{5x}{4}$