the complete question in the attached figure
we know that
C is the midpoint of parallelogram WXYZ
so
WC=CY
WC=x+4
CY=2x-7
then
x+4=2x-7----------------> 2x-x=4+7-------------> x=11
CY=2x-7------------> CY=2*11-7---------> CY=22-7----> CY=15 ft
the answer is
CY=15 ft
