Question

quanto é 10x+40=20x-40

Answer 1

$10x + 40 = 20x - 40 \\ 10x - 20x = - 40 - 40 \\ - 10x = - 80 \\ 10x = 80 \\ x = \frac{80}{10} \\ x = 8$

Answer 2

$10x - 20 x = - 40 - 40$
10x = -80
x = 80/10 = 8