280 + $\frac{x}{x+520}$ = 141 + 65 × 8
280 + $\frac{x}{x+520}$ = 141 + 520
280 + $\frac{x}{x+520}$ = 661
$\frac{x}{x+520}$ = 661 - 280
$\frac{x}{x+520}$ = 381
x = 381 × (x+520)
x = 381 × x + 198120
x - 381 × x = 198120
x × (1 - 381) = 198120
x × -380 = 198120
x = 198120 : -380
x = $\frac{-9906}{19}$