Giải thích các bước giải:
`c)`
`2/3xx4/x xx1/5=4/45`
`=>(2/3xx1/5)xx4/x=4/45`
`=>2/15xx4/x=4/45`
`=>4/x=4/45:2/15`
`=>4/x=4/45 . 15/2`
`=>4/x=2/3`
`=>x2=4.3`
`=>x2=12`
`=>x=6`
`d)`
`3/4xx x/5=5/2xx9/10`
`=>3/4 xx x/5=9/4`
`=>x/5=9/4:3/4`
`=>x/5=9/4 . 4/3`
`=>x/5=3`
`=>x/5=15/5`
`=>x=15`