Question 1205894
t, some time unit
Speed for A, {{{8/t}}}
Speed for B, {{{12/t}}}
x, the time for B to close the initial 84 feet distance from A.


{{{(12/t-8/t)x=84}}}, again t is just a time unit; not a variable.


{{{x=84/4}}}


{{{x=21}}} time units B to catchup to A.



Distance A traveled during the catchup time:
{{{(8)(21)=highlight(168)}}}