The polygon angle sum theorem states that the sum of the measures of the interior angles of an n-gon is

n-2/180

(n-1) 180

180/n-1

(n-2) 180

D.

Step-by-step explanation:

The formula is Sum(n) = (n -2) 180.

we have three similar triangles, because each has a right angle and shares an angle.   let's write the angles in order: opposite to short leg, long leg, hypotenuse.

cab similar to bad similar to cbd

or as ratios,

ca: ab: cb = ba: ad: bd = cb: bd: cd

we also know

ac = ad + cd

(ad+cd): ab: cb = ba: ad: bd = cb: bd: cd

(ad+cd)/cb=cb/cd

we have cb=6, ad=5 and seek x=cd.

we reject the negative root and conclude x=4

answer: 4