7=1++4
9=4++3
9=+2+5
8=+4+3
2+5+310
9-4-2=
3+4+17
2+7+1=
①39+28=
②83-56=
③90-42=
④74-18=
⑤70-24-16=
⑥28+36+19=
⑦46+(32-18)=