2.2*(-2.1)+1.21*4.2-2.1*0.22
=-2.2*2.1+1.21*4.2-2.1*0.22
=-2.2*2.1+1.21*2*2.1-2.1*0.22
=-2.2*2.1+2.42*2.1-2.1*0.22
=2.1*(-2.2+2.42-0.22)
=2.1*0
=0