The diagonals on any parallelogram always <em>bisect </em>each other - cut each other in half. The two diagonals on URTS are <em>RT </em>and <em>US</em>. <em>US</em> cuts <em>RT</em> into two equal segments, <em>RQ </em>and <em>QT,</em> each of which is half of <em>RT</em>. So <em>QT</em> must be half of <em>RT</em>, and since RT = 10, QT = 5.
