Can you explain number 9 on P. 72 of PWN the SAT 4th edition?

Sure. Recognize that simplifies to , so you can rewrite the first equation thusly: . Since there’s a  in every term, you can just divide the whole equation by  to eliminate the darn things! The equation simplifies to .

From there, this is a pretty easy problem. Solve for x by elimination:

From there, continue to solve for y:

The question asks you for the sum of the coordinates of the ordered pair that satisfies the system of equations, so you have to add:

Gridding in either the fraction or the repeating decimal is fine as long as you fill all the boxes with the decimal (i.e., you enter “1.11”).