a)
2x - 2 = 12 - 5x
2x + 5x = 12 + 2
7x = 14
x = 14/7
x = 2
b)
x - 39 = - 79
x = -79 + 39
x = -40
c)
10 = x + 8
10 - 8 = x
2 = x ou x = 2
