(120x)^1/2 see attached photo for steps
After Sally had given 1/9 of her stamps to Andy, she had 280 stamps (since they now have equal shares). So 280 was 8/9 of what she started with, making the 1/9 she handed over equal to 280/8, that’s 35. And Andy was “under” by the same amount she was “over” an equal share, that’s 35 under matching her 35 over, which is 70 altogether.
By all means use algebra but you may find you can reason a word problem through in words.
It would be (0,-4).
If you do 9(0) + 7(-4) it would be 0 + -28 which equals -28.
