Circle theorem: angle in a semi-circle is a right angle.Therefore angle BAE = 90 + 31 = 121 degrees ABDE is a cyclic quadrilateral and:Circle theorem: Opposite angles in a cyclic quadrilateral sum to 180 degrees.BAE is opposite CDE.CDE = 180 -121 = 59 degrees Therefore EDA = 59-18 = 41 degrees.