You could easily change the 2 1/2 to a 2.5 and do 2.5-6=-3.5
The table is proportional, cause there all plus four.
-2 + 4 = 2
0 + 4 = 4
2 + 4 = 6
4 + 4 = 8
Hope it helps
If you use a proportion, you'll get:

Then, you use cross products:

Then, you algebraically solve x:

The answer is 5/3 inches , or 1 5/13 inches, or 1.6 repeating.
The greatest number common to 50 and 10 is 10
10 is the answer
hope this helps