①75%x=360
②(1-55%)x=90
③31%x-66=8.4
④25%x+50%x=420
8.1-0.03=
13+62+15=
0.3×0.3=
8×25%=
+=
-=
×=
40×0.3=
12÷2.5=
3.14×9=
3.14×7=