B. 31°, 43°, 106°
since all angles of a triangle add up to 180°, you combine all of the equations to equal 180 and solve for X. the equation you would get it 3x+1+11x-4+5x-7=180. this simplifies to 19x-10=180. then you solve for x, and it is 10. then, you plug 10 into all of the equations separately to find the angles. therefore, the answer is B