4x 42 + 42 = 40 5 - 20

168x + 42 = 200 - 20

168x + 42 = 180

168x = 180 - 42

168x = 138

x = 138 / 168

x ≈ 0.8214285714

Проверка:

4 0.8214285714 42 + 42 = 40 * 5 - 20

142.8571428 + 42 = 200

184.8571428 = 200

Уравнение верное.