You can put this solution on YOUR website!
7 is 3 units from 4 and 2 units from 9.
So it's 3/5 of the way from 4.
So let's try
So now you're in the neighborhood.
Increase the value slightly and see how much closer you get to 7.
2.62?
2.64?
Keep trying those values until you get as close to 7 as you like.