1) 2x + 4*(40-x) = 100
2x + 160 - 4x = 100
-2x + 160 = 100
-2x = -60
x = 30

Ответ: x = 30

2) 4x + 2*(40-x) = 100
4x + 80 - 2x = 100
2x + 80 = 100
2x = 20
x = 10

Ответ: x = 10