Can you explain number 7 on P. 72 of PWN the SAT 4th edition? Thank you.

Yep! Use elimination again here. Recognize that if you multiply the first equation by 5, you’ll have the easy opportunity to eliminate the x-terms.


From there, you know that y = 1, so you know the answer must be A because no other choice has 1 for its y-coordinate. Might as well keep solving for x to be sure, though…