Part (i):
Let's list the lengths of the sides of triangle ABD in order from shortest to longest: 2 cm, 5, cm, 6 cm.
Now let's do the same for triangle DCB: 6 cm, 15, cm, 18 cm.
Let's divide the length of each side of triangle DCB by the length of the corresponding side of triangle ABD (I'll leave the cm units off for convenience):
6/2 = 3
15/5 = 3
18/6 = 3
The ratios are all 3. By SSS Similarity, the triangles are similar.
Part (ii):
From the proof above, we can write the correct statement of similarity.
Triangle ABD is similar to triangle DCB
From the statement of similarity, angles A and BDC are corresponding angles, so they are congruent.
m<DAB = m<BDC = 110.5 deg