9) ∠14 and ∠12 are formed by transversal b. They are alternate angle.
10) ∠3 and ∠18 are formed by transversal a. They are interior angles of same side.
11) ∠10 and ∠20 are formed by transversal d. They are alternate angles.
12)∠4 and ∠16 are formed by transversal c. They are corresponding angles.
What is transversal?
From the figure
∠14 and ∠12 are formed by transversal b. They are alternate angles because they are at opposite sides of the transversal b.
∠3 and ∠18 are formed by transversal a. They are interior angles of same side because they are within the parallel lines and at the same of the transversal.
∠10 and ∠20 are formed by transversal d. They are alternate angles because they are formed at the opposite sides of the transversal.
∠4 and ∠16 are formed by transversal c. They are corresponding angles. The are at the corresponding sides of the transversal and the lines a and b it bisect.
Values of these angles are equal only and if only the transversals intersect parallel lines.