Answer:
D. 10.2
Explanation:
Since the triangle is a right triangle we can use the Pythagorean theorem.
I will call the hypotenuse
, so in this case:

and one leg will be
, in this case:

and the unknown for this problem is the other leg which in the image is called
.
So the formula for the Pythagorean theorem:

clearing for x:

substituting
and
:

the value of x is option D. 10.2