Answer:
Step-by-step explanation:
It is a pity that we can't see the name of the units on the y axis. I sound like a grumpy old man (which I am), but the answer might be easy enough. Follow the line upwards from x=3 to the best fitting line. Then go left until you hit the y axis.
All other things being equal, you should get 6. I'm not positive about this because the units are differently spaced along each axis. But I do think you have the right equation y = -x + 9
