Respuesta :

40 - 3k + 10k = -10 - 8k - 10

40 + 7k = -10 - 8k - 10

40 + 7k = -8k - 20

40 + 7k - 40 = -8k - 20 - 40

7k = -8k - 60

7k + 8k = -8k - 60 + 8k

15k = -60

15k/15 = -60/15

k = -4