Supplementary angles
x+20+5x+10=180
6x+30=180
6x=150
x=25
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There is a mistake 9,12,13 is not a right triangle. but 9,12,15 is. IF you use this triangle instead, then the area of the 13,14,15 triangle is the sum of the area of the other two triangles.
Given:
The given inverse trigonometric term is:

To find:
The value given inverse trigonometric term.
Solution:
We have,

Using the calculator, we get


The value of given term is 31.1°.
Therefore, the correct option is B.
I hope my explanation helps