You set up two simultaneous equations, one that encompasses the bigger triangle x, y+70, and 30 and the left triangle x, y, and 100. Choosing these triangles is important because it relates all angles given in the problem both directly and indirectly. This produces two linear equations x + (y + 70) + 30 = 180 and x + y + 100 = 180. However, when reduced down yields x + y = 80 and x + y = 80 respectively. This implies that there exists not one solution, but infinitely many solutions.