Use a ruler, a compass, and a protractor to construct triangles with the following characteristics. In each case, discuss whether or not all triangles with those characteristics are congruent.    Triangle ABC has a side AB of length 6 cm, the angle at A is 50° and the angle at B is 120°.   Triangle DEF has a side DE of length 7 cm, the angle at D is 15°, and side EF is 6 cm.   Triangle GHI has side GH of length 5 cm, the angle at H is 50°, and side HI is 8 cm.