解方程. 42:6=x:80%; 0.36×5﹣2x=0.4.
16-1= 16-3= 16-5= 16-4= 16-0= 16-2=
17-2= 17-4= 18-6= 12-1= 7-5= 12-2=
9-3= 9-5= 18-2= 11-1= 9-6= 9-1=
19-4= 19-6= 16-5= 16-4= 16-0= 16-2=
7+2= 2+5= 12+5= 11+1= 7+3= 12+1=