Answer:
 105 seconds
Step-by-step explanation:
We can use the relation ...
 distance = speed · time
to write equations for the distance each girl travels as a function of time t since Jillian started.
 Jillian's distance = (6 ft/s)(t)
 Samantha's distance = (7 ft/s)(t -15) . . . . Samantha starts 15 seconds after the clock starts running
These distances are the same when ...
 6t = 7(t -15)
 6t = 7t -105 . . . . eliminate parentheses
 105 = t . . . . . . . . add 105-6t
Jillian had been walking 105 seconds when the two girls met.
