3x = 28 - x 5x + 12 = 8x + 30 33 + 8x = -5x + 72
3x + x = 28 5x - 8x = 30 - 12 8x + 5 x = 72 - 33
4x = 28 -3x = 18 13x = 39
x = 28 : 4 x = 18 : (-3) x = 39 : 13
x = 7 x = -6 x = 3
7 - 2x = 3x - 18 2x + 9 = 2x - 4
7 + 18 = 3x + 2x 13 = 2x - 2x
5x = 25 13 = 0
x = 25 : 5 ∅
x = 5
15:5
10:2
20:4
15:3
9:3
16:2
18:2
4:2
100:5
8:2
25:5
20:4
8:8
22:2
(197+112)+197=506 (кресел)
Ответ: 506 кресел продала фирма.