19991+199.1+19.91+1.991
=20000-9+200-0.9+20-0.09+2-0.009
=20222-9.999
=20212.0001
88.88*0.9+22.22*6.4
=22.22x4x0.9+22.22x6.4
=22.22x(3.6+6.4)
=22.22x10
=222.2