see the attached figure with letters
we have that
cos(alfa) triangle ABD=12/y
and
cos(alfa) triangle ABC=y/28
then
12/y=y/28----------> y²=12*28=336----------> y=√336=4√21
y=4√21
applying the Pythagorean theorem triangle ABC
(16+12)²=x²+y²----------? x²=28²-(4√21)²--------> x²=784-336
x=√448=8√7
the answer is
x=8√7
y=4√21