a ) $\frac{x + 1}{9}$ + $\frac{x + 2}{8}$ = $\frac{x + 3}{7}$ + $\frac{x + 4}{6}$
⇔ $\frac{(x +1) . 8 .7 . 6 }{9 .8 .7 . 6 }$ + $\frac{ (x + 2 ). 9 . 7 . 6 }{9 . 7 .8 .6 }$ = $\frac{( x + 3 ) . 9 . 8 . 6 }{9 . 7 . 8 . 6}$ + $\frac{ ( x + 4 ). 9 . 8 .7 }{9 . 8 . 7 . 6}$
⇔ 336x + 336 + 378x+ 756 = 432x + 1296 + 504x + 2016
⇔ 1650x + 4404 = 0
⇔ x = 734 / 275