Answer:
D.
![x=6](https://img.qammunity.org/2020/formulas/mathematics/middle-school/iytjkob8c453cdntkigo6vyjyk3yzlat9o.png)
Explanation:
We have been given an image of two triangles. We are asked to find the value of x for our given triangle.
We know that altitude of a right triangle to its hypotenuse divides right triangle into two triangles, that are similar to original triangle and each other.
Using similarity, the hypotenuse of smaller triangle (x), will be proportional to hypotenuse of original triangle.
The leg (x) of original triangle will be proportional to leg (4) of smaller triangle.
![(x)/(5+4)=(4)/(x)](https://img.qammunity.org/2020/formulas/mathematics/middle-school/x858n9aumqo6zk7sfmq4008ewp9l5yefo2.png)
![(x)/(9)=(4)/(x)](https://img.qammunity.org/2020/formulas/mathematics/middle-school/x7iewhn0q9vpjfd7bw7n0z0glp4lu1b1f2.png)
Upon cross multiplying our equation, we will get:
![x^2=36](https://img.qammunity.org/2020/formulas/mathematics/middle-school/6ghlac9a78mxje12efm2gpqv3lqf7po5s3.png)
Now, we will take square root of both sides of our equation as:
![x=√(36)](https://img.qammunity.org/2020/formulas/mathematics/middle-school/waio2b42zpfk7i4ccn0ikg1qjtfhyi1iy5.png)
![x=\pm 6](https://img.qammunity.org/2020/formulas/mathematics/middle-school/h9kgvdg60nfxyoddublxzx3avjmz3m85re.png)
Since length cannot be negative, therefore, the value of x is 6 and option D is the correct choice.