30-7.2/(7.2/30+0.06)=30-7.2/(0.24+0.06)=30-24=6天
7.2÷30=0.24(千米)0.24+0.06=0.3(千米)7.2÷0.3=24(天)30-24=6(天)
30-7.2÷(7.2÷30+0.06)=30-7.2÷(0.24+0.06)=30-7.2÷0.3=30-24=6(天)