METHOD ONE:
If any 2 lines are parallel, they must form the same slope if they were in the xy coordinate plane. So we can see that lines l and m are forming the same slopes as the two sides on the right and bottom of the equilateral triangle. So we can see that whatever angle l and m form with each other, must be the same as the angle that the lower right hand angle in the equilateral triangle is forming. Since equilateral triangles only have 60° angles, x must be 60°, so the answer is C.
METHOD TWO:
Imagination! If we imagine that we sort of slide lines l and m together directly upwards, eventually line m will be exactly overlapping with line AC. Then if we imagine that we scroll lines l and m to the left, eventually they will perfectly overlap the lower right hand corner of the equilateral triangle. Since this angle must be 60°, so must x, so the answer must be C.
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