In the diagram below of triangle
U
V
W
UVW,
X
X is a midpoint of
U
V
‾
UV
and
Y
Y is a midpoint of
V
W
‾
VW
. If
X
Y
=
21
−
4
x
XY=21−4x, and
U
W
=
x
+
24
UW=x+24, what is the measure of
X
Y
XY?