in any triangle, the sum of the angles always equals 180°. therefore, to find angle a you would first add each angle together and set it equal to 180. for ex for number 29 you would write out 2x+80 + x+60 +40 = 180. solve that equation out for x. plug the x value in for x in your equation for angle a so for 29 you plug your x value into the equation x+60. that’s your answer hope that helped!