F= 6.
-7f -9=9-4f
3f-9=9
3f=18
F=6
You could draw a linear model to express the relationship. The y value will be your inch(es) while your x is your feet. Since one foot has 12 inches, then your slope is 12.
Well 12 divided by 6 is 2 so what do you think would be the easiest model to make