Answer:
9
Step-by-step explanation:
the triangle is right angle.
at right angle it makes 90°. therefore;
(3d+1)°+(6d+8)°=90°
3d+1°+6d+8°=90°
9d+9°=90°.
9d=90°-9°
9d=81°
d=81/9
d=9°
