Explanation:
always consider : the bigger an angle, the longer the opposite side.
the smallest angle here is 42°, so the shortest side is opposite of these 42°, and that is JL (the shortest side going into the first box).
the next large angle is 58°, so the opposite side KL is going into the second box.
the largest angle is 80°, and its opposite side JK is therefore the largest side and goes into the third box.