1) The triangles are similar, so correponding sides have the same ratio.
.. 3x/20 = (4x +2)/28
.. 3x/5 = (4x +2)/7 . . . . . . . multiply by 4
.. 7*3x = 5(4x +2) . . . . . . . multiply by 35 = 5*7
.. 21x = 20x +10 . . . . . . . . eliminate parentheses
.. x = 10 . . . . . . . . . . . . . . . subtract 20x
2) The triangles are similar, so corresponding measures have the same ratio.
.. x/42 = 10/15
.. x = 42*(10/15) = 28
3) The third angle of triangle ABC is 180° -20° -80° = 80°. Then two of the angles of ABC match those of JKL. The 3rd answer selection is appropriate.