Answer :
i think it's something like this:
210=70%
x=100%
210(mile):7=30mile
10%=30mile
30×10=300mile
300-210=90mile
I don't know if it's true, I used to do it like this i think
210=70%
x=100%
210(mile):7=30mile
10%=30mile
30×10=300mile
300-210=90mile
I don't know if it's true, I used to do it like this i think