B)
Given that angles (3x -10) and x are complementary, then we can write the following equation:
(3x -10) + x = 90º Definition of Complementary angles
3x-10 +x = 90º Combine like terms
4x -10 = 90 Add 10 to both sides
4x=100 Divide both sides by 4
x=25º
2) So , Angle x = 25º and m angle 3x- 10 is 65º