Answer: 25cm²
Explanation:
Ok, so I haven't actually learnt this in school so I'm going to give it my best shot. (Don't be surprised if I get this wrong though.)
So, Quadrilaterals A and B are similar. They have the same angles. Therefore, (I'm thinking that) Quadrilateral B is just a scaled-up version of Quadrilateral A.
Here comes my theoretical part:
If one side of Quadrilateral B is 5 times longer than the same side of Quadrilateral A...
(Quadrilateral A is 3cm, and Quadrilateral B is 15cm).
... then the area of the entire Quadrilateral B should just be 5 times bigger than Quadrilateral A.
Therefore, (I'm guessing), Quadrilateral B has an area of 25cm²