If x=3 then the f(x)=4
If x=6 then the f(x)=7
If x=7 then the f(x)=8
The ratio is 2 1/4:1/2, and for everything you do to one side, you do to the other, so, 2 1/4* 1.77777778=4, so 1/2*1.77777778=0.88888889
The answer to your question is 5.875
I'd say centimeters, if that's what you're looking for. Maybe 1-2 cm.