Question 976391
A, B, aircraft,... what?


Give the full problem description and question.


(Enough now understood)
The description does not say, "catch up"; but only asks what is their separation in distance after 7 minutes.


___________________rate___________time__________distance
craftA_____________300_____________7____________{{{A}}}
craftB_____________240_____________7____________{{{B}}}


A and B are also being used in this solution as the distances gone, for each aircraft.  Note that  you can make a number line to show the relative initial positions of craft A and craft B.


{{{system(A=300*7=2100,B=240*7=1680)}}}.


Zero on the number line is where A starts.  18 on the number line is where B starts.  Each goes in the same direction, toward the greater values of the number line.


aircraft A:  went 2100 miles ON THE NUMBER LINE.
aircraft B:  went to 1680+18=1698 ON THE NUMBER LINE, since it started AT 18.


The separation now is that A is AHEAD of B by  2100-1698=402 miles.