Answer:
![x = (147)/(13)](https://img.qammunity.org/2021/formulas/mathematics/high-school/nmpop1bo52ikm1iamvk3wne5waal613f9d.png)
Explanation:
Please refer to attached for labeling of the diagram:
We have 2 triangles here in the figure:
.
1.
is common to both the triangles.
Sides AC || DE (parallel sides):
So, Corresponding angles will be equal
2.
![\angle A = \angle D](https://img.qammunity.org/2021/formulas/mathematics/high-school/o9i99y7mpey7w2d2scqf0ilt3m6w5jg4a9.png)
3.
![\angle E = \angle C](https://img.qammunity.org/2021/formulas/mathematics/high-school/qb7ky5rjn6six7x3hmpididxr05nxom0vg.png)
So,
are similar to each other.
Similar triangles have ratio of their sides as equal.
So,
![AB : BD = BC : BE](https://img.qammunity.org/2021/formulas/mathematics/high-school/9jtm6ghey1mwue66tq3dt7o71cd850oibs.png)
![\Rightarrow (6+7)/(6) = (21)/(21-x)\\\Rightarrow (13)/(6) = (21)/(21-x)\\\Rightarrow 13 * (21-x) = 21 * 6\\\Rightarrow 13x = 7 * 21\\\Rightarrow x = (147)/(13)](https://img.qammunity.org/2021/formulas/mathematics/high-school/z06ojubxyky5u4i7jos14sioymhydfap4z.png)
Hence,
![x = (147)/(13)](https://img.qammunity.org/2021/formulas/mathematics/high-school/nmpop1bo52ikm1iamvk3wne5waal613f9d.png)