a negative 3 plus another negative 6 is a negative 9. Is just like if you borrow $3 from your friend and borrow $9 from another friend. That means you own two of your friends a total of $9. This can be mathematically illustrate as: -3 + (-6)= -9
It would be (6,9) from the given end point to the given middle point it is a 7 point difference, so we add 7 to the y value to get the other endpoint, hope it helps!
