Answer:
Option C. x = 5
Explanation:
To solve this question we should always keep these two points in our mind.
1). In-center of a triangle is formed by the intersection of the angle bisectors of all interior angles of the triangle.
2). In-center of a triangle is equidistant from all three sides of the triangle.
From the figure attached,
In ΔSRT,
∠ASZ ≅ ∠ZSB [ SZ is an angle bisector of angle ASB]
5x - 9 = 16 [ given in the question]
5x = 16 + 9
5x = 25
x =

x = 5
Therefore, Option C. is the answer.