①x÷7+3×0.9=4
x÷7=4-3×0.9
x÷7=4-3.6
x÷7=0.4
x=0.4×7=2.8
②3（0.72-x+1）=4.8
0.72-x+1=1.6
x=0.72+1-1.6=0.12oo,谢谢你