AEB is a right isoceles triangle. It means that it is half a square. So, AB is the diagonal of the square with side AE.
The side and diagonal of a square are linked by the following formula:
![d = l√(2)](https://img.qammunity.org/2019/formulas/mathematics/middle-school/iepe2yp4fvf5nxnnab1x0mr1eqboxr21bu.png)
which means
![18√(2) = l√(2)](https://img.qammunity.org/2019/formulas/mathematics/middle-school/n5myxzrgf91qq2sfiakwpo02k7whtdqy3q.png)
and this AE=EB=18.
The area of a parallelogram is given by the multiplication of the base and the height, which in our case means
![A = \overline{BD}\cdot\overline{EB} = 18\cdot 28 = 504](https://img.qammunity.org/2019/formulas/mathematics/middle-school/lao1ez9063wsp1or85lv1tuqgkg5lcjkc5.png)