Here, triangle AEN and ALG are similar.
We know that the ratio of corresponding sides of two similar triangles are equal. So,
[tex]\frac{21}{42} =\frac{2x-9}{(2x-9)+(x+7)}\\\\\frac{1}{2} =\frac{2x-9}{3x-2}\\\\ 3x-2=4x-18\\\\-2+18=4x-3x\\\\16=x\\\\x=16\\[/tex]
