[tex]\frac{2x}{7} - \frac{x}{4} = \frac{3}{28} \\\\\frac{2x*4}{7*4} -\frac{7x}{4*7} = \frac{3}{28} \\\\\frac{8x}{28}-\frac{7x}{28} =\frac{3}{28} \\\\\frac{8x-7x}{28} = \frac{3}{28} \\\\\frac{x}{28} = \frac{3}{28}[/tex]

x=3