`***`
`a)`
   `10cm^2``6mm^2=.........mm^2`

   `10cm^2=10xx100=1000mm^2`

  `->10cm^2``6mm^2=1006mm^2`
`b)`
   `1dm^2``98cm^2=......cm^2`

   `1dm^2=100cm^2`

  `->1dm^2``98cm^2=198cm^2`
`c)`
   `12m^2``5dm^2=.....cm^2`

   `12m^2=12xx10000=120000cm^2`

   `5dm^2=5xx100=50cm^2`

  `->12m^2``5dm^2=120500cm^2`
`d)`
   `60km^2``8ha=....m^2`

   `60km^2=60xx1000000=60000000m^2`

   `8ha=8xx10000=80000m^2`

  `->60km^2``8ha=60080000m^2`
`-----------`
Công thức
   `+1km^2=1000000m^2`

   `+1ha=10000m^2`

   `+1m^2=10000cm^2`

   `+1dm^2=100cm^2`

   `+1cm^2=100mm^2`