Answer is 6-3/4 ft for missing side
Step by step. Assuming the table is rectangular in shape, the one given length of 4-1/4 Ft x 2 sides = 9-1/2 ft.
23 ft - 9-1/2 ft = 13-1/2 ft left for the other two sides.
13-1/2 ft divided by 2 = 6-3/4 Ft is the missing length.