We know that DO and OX have equal side lengths. Since DX's length is 13, we divide 13 by 2 to get 6.5 as our answer for length OX. We also know that DO's length is also 6.5 because when we add 6.5 by 6.5, we get 13 as our total length of DX.
6.5 rounded to is 7.
So, length OX is 7 when rounded and that would be your answer.