Because the diagonal of the diamond is vertical. So the diamond can be regarded as four congruent right-angled triangles.

Because the four sides of the diamond are equal in length, it becomes 5.

According to Pythagorean theorem, the other diagonal is 3*2=6.

The area is half of the two diagonal fractions. This is 24.

The length of the hypotenuse is 13. According to Pythagorean Theorem, the median line on the hypotenuse of a right triangle is equal to half of the hypotenuse, so it is 6.5.