x- nr
[tex] \frac{x}{2} + \frac{x}{4} = 390[/tex]
[tex] \frac{4x + 2x}{8} = 390 \times 8[/tex]
[tex]6x = 3120[/tex]
[tex]x = 3120 \div 6[/tex]
[tex]x = 520[/tex]
Verificare
[tex] \frac{x}{2} = \frac{520}{2} = 260[/tex]
[tex] \frac{x}{4} = \frac{520}{4} = 130[/tex]
[tex] \frac{x}{2} + \frac{x}{4} = 260 + 130 = 390[/tex]