Answer:
15
Step-by-step explanation:
Consider right triangle EFD. The sum of the measures of all interior angles in triangle EFD is 180°, so
[tex]m\angle FED=180^{\circ}-90^{\circ}-3x=90^{\circ}-3x[/tex]
Consider right triangle EBC. The sum of the measures of all interior angles in triangle EBC is 180°, so
[tex]m\angle BCE=180^{\circ}-(90^{\circ}-3x)-90^{\circ}=3x[/tex]
Consider triangle ACD. The sum of the measures of all interior angles in triangle ACD is 180°, so
[tex]x+8x+3x=180^{\circ}\\ \\12x=180^{\circ}\\ \\x=15[/tex]
