1:6.98-x=5.7 x=6.98-5.7 x=1.28
2:83-x=38 x=83-38 x=45
3:27.2/x=6.8 x=27.2/6.8 x=4
4:7.8/x=1.3 x=7.8/1.3 x=6
( / 是除号 )