From the given pair of triangles  .

Since all right angles are congruent, .

So, by AA similarity postulate, .

Using th definition of similar polygons, .

                      (Write the proportion)

                      (Substitute )

                   (Cross product)

                      (Multiply)

                              (Divide each side by 15)

Since , .

The value of x is 9. The measure of DE is 9.