3.9*1.4+2*1.8
=(4-0.1)*1.4+2*(2-0.2)
=4*1.4-0.1*1.4+2*2-2*0.2
=5.6-0.14+4-0.4
=(5.6+4)+(-0.14-0.4)
=9.6-0.54
=9.06