Question 12391
Since U is the midpoint of XY, you know that XY is exactly two times UY.  In order to set these equal to one another, multiply UY by two and put it equal to XY.  You get the equation:  {{{16x - 6 = 2(4x+9)}}}.  Use the distributive property to begin solving, so you get {{{16x - 6 = 8x+18}}}.  Combine like terms to get {{{8x = 24}}}.  Then solve for x (x=3).

To find the measure of XY, plug 3 in for x in the formula:  16(3) - 6 = XY.  Work it out to get XY = 42.