see the attached figure below to better understand the problem
give me a minute to draw the figure
In this problem, we have that
triangle AOC is congruent with triangle EOC
because
if OB is perpendicular to AC
then
OD is perpendicular to EC too
because
OB=OD
so
DC=ED -----> given
ED=7
DC=7
EC=7+7=14
AC=EC=14
therefore
x=14