Solution

Let $$\angle A = 3x$$ and $$\angle B = 2x$$

$$\angle A + \angle B = 180$$
(Adjacent angle : Supplementary)

$$3y + 2x \Rightarrow 5x = 180\Rightarrow x = \dfrac {180}{5}$$

$$x = 36^{\circ}$$

$$\angle A = \angle C = 3x = 3\times 36$$

$$= 108^{\circ}$$

$$\angle B = \angle D = 2x = 2\times 36 = 72^{\circ}$$