Answer :
We have
18 minutes to walk to school
18 minutes to walk back home
In a day we walks 18+18=36 minutes
If he walks 21 days
21 x 36= 756 minutes
as we can see the number that eestimates better the number of minutes is 800 minutes
We have
18 minutes to walk to school
18 minutes to walk back home
In a day we walks 18+18=36 minutes
If he walks 21 days
21 x 36= 756 minutes
as we can see the number that eestimates better the number of minutes is 800 minutes