Since ABCD is a parallelogram, the opposite sides will be parallel and equal,

Consider that AC acts as a transversal to the parallel lines AB and CD, so we can write,

So by the ASA criteria, the triangle AED is congruent to the triangle CEB,
Then the corresponding parts of the triangles will be equal,

Hence Proved.
3.15 will be your answer i am very sure of that
15/8 is already an improper fraction, if you want a proper fraction the answer is 1 and 7/8