You start by writing an algebraic equation:
0.6m+1.5=13.5
‘m’ represents the amount of minutes
Then you simply solve it:
0.6m+1.5=13.5
-1.5 -1.5
_____________
0.6m= 12
/0.6 /0.6
_____________
m=20
It took 20 minutes for the person to reach the airport.
Hope this helps :)