That answer is incorrect.
Since this triangle starts at the exact centre of the circle, both of the “arms” are radii of the circle (and therefore the same length), making this an isosceles triangle (two equal sides). In isosceles triangles the angles UNDER those two sides are also identical (therefore 20 degrees in this case). The final angle must add with those two 20’s to a total of 180 degrees. Two 20 degree angles = 40, so c must equal 140 degrees. B is 40. E and d are 20.