A18= matrix([[0,2.2,1.5,-3.3],[0.2,1.8,0,4.2],[-1,-3.1,2.5,0],[0.5,0,-3.8,1.5]]) 
b18= vector([-9.3,9.24,-8.70,11.94]) 
x18= A18.solve_right(b18) 
print x18