[tex] x=numarul\;de\;locuri\;din\;avion \\ \\ \frac{2}{3}x+20= \frac{3}{4}x \\ \\ \frac{3}{4}x-\frac{2}{3}x=20 \\ \\ (\frac{3}{4}-\frac{2}{3})x=20 \\ \\ (\frac{3*3}{4*3}-\frac{2*4}{3*4})x=20 \\ \\ (\frac{9}{12}-\frac{8}{12})x=20 \\ \\ \frac{9-8}{12}x=20 [/tex]
[tex] \frac{1}{12}x=20 \\ \\ x = 12*20=\boxed{240\;locuri\;in\;avion}[/tex]