Solution

Let $$\angle A$$ and $$\angle B$$ are two adjacent angles.
But we know that sum of adjacent angles of a parallelogram is $$180^o$$
$$\angle A+ \angle B=180^o$$
Given that adjacent angles of a parallelogram are in the ratio $$4:5$$ and let that ratio be multiple of $$x$$
$$\angle A+\angle B=180^o$$
$$4x+5x=180^o$$
$$9x=180^o$$
$$x=180/9$$
$$x=20^o$$
$$\angle A=4x=4 \times 20=80^o$$
$$\angle B=5x=5 \times 20=100^o$$
Also $$\angle B +\angle C=180^o$$ [Since $$\angle B$$ and
$$\angle C$$ are adjacent angles]
$$100^o+\angle C=180^o$$
$$\angle C=180^o-100^o=80^o$$Now, $$\angle C+\angle D=180^o$$ [Since $$\angle C$$ and
$$\angle D$$ are adjacent angles]
$$80^o + \angle D=180^o$$
$$\angle D=180^o-80^o=100^o$$