from numpy import *
from numpy.linalg import *
saida = array([50, -120, 350, 870])
saida = saida.T
eq = array([[1, -1, 0, 0],[0, 1, -1,  0],[0, 0, 1, 0],[1,0,0,1]])
saida = dot(inv(eq),saida)
print(saida)