bonsoir
5 x - 1 = 2 x + 15
5 x - 2 x = 15 + 1
3 x = 16
x = 16/3
5 * 16/3 - 1 = 2 * 16/3 + 15
80/3 - 3/3 = 32/3 + 45/3
77 = 77