So firstly, we have to find the LCD, or lowest common denominator, of 9 and 7. To do this, list the multiples of 9 and 7 and the lowest multiple they share is going to be your LCD. In this case, the LCD of 9 and 7 is 63. Multiply x^2/9 by 7/7 and 2y/7 by 9/9:
[tex] \frac{x^2}{9}\times \frac{7}{7}=\frac{7x^2}{63}\\\\\frac{2y}{7}\times \frac{9}{9}=\frac{18y}{63}\\\\\frac{7x^2}{63}+\frac{18y}{63} [/tex]
Next, add the numerators together, and your answer will be: [tex] \frac{7x^2}{63}+\frac{18y}{63}=\frac{7x^2+18y}{63} [/tex]
