20 because if 9 is 45% than 1 person is equal to 5%. and if you added one more person to make 10 it would be half which is 50%. so 10+10=20 which = 100%
We can use Law of Cosines to solve for the angle of Z. The solution is shown below: cos C=(a²+b²-c²)/2ab cos Z = (yz² + xz² - xy² )/2*yz*xz cos Z = (20² + 25 - 13²)/2*20*25 cos Z = 856 / 1000 Z=31.13°
