In triangle STU, we have ST = SU = 22 and TU = 8. Let M be the midpoint of \(\overline{ST}\) and N be on \(\overline{TU}\) such that \(\overline{SN}\) is an altitude of triangle STU. If \(\overline{SN}\) and \( \overline{UM}\) intersect at X, then what is SX?