Convert the following into decimals and add:
$26 \mathrm{km} 46 \mathrm{m}$ and $68 \mathrm{km} 528 \mathrm{m}$

Convert the following into decimals and subtract:
$6 \mathrm{km} 45 \mathrm{m}$ and $68 \mathrm{km} 500 \mathrm{m}$

Note: write only the numerical answer excluding units.