Răspuns :
x / 5 = x -80 aducem la acelasi numitor
x = 5x - 400
- 4x = - 400
x = 400 / 4
x = 100
verificare: 100 / 5 = 20 si 100 - 80 = 20
x = 5x - 400
- 4x = - 400
x = 400 / 4
x = 100
verificare: 100 / 5 = 20 si 100 - 80 = 20