$a, -4 (x +1) +89x -3 = 24$
$⇒ -4x -4 +89x -3 = 24$
$⇒ 85x = 24 +7$
$⇒ 85x = 31$
$⇒ x = \frac{31}{85}$
$Vậy$ $x = \frac{31}{85}$
$b,(x+1)+(x+2)+(x+3)+(x+4)+...+(x+1000) = 5750$
$⇒ (x +x +x +....+ x) + (1 +2 +...+1000) = 5750$
$⇒ 1000x + \frac{(1000 +1).1000}{2} = 5750$
$⇒ 1000x + 500500 = 5750$
$⇒ 1000x = -494750$
$⇒ x = -494,75$
$Vậy$ $x = -494,75$