Marita runs clockwise around a track in 40 seconds. jill leaves from the same point, but runs counter clockwise. she meets marita every 15 seconds. how long does it take jill to run around the track

He takes 9,375 seconds in running the track
explanation:
in 15 seconds she runs 15/40 of the track wich is equal to 3/8 so he runs 1 3/8 of a track in only 15 seconds, so he runs the track 3/8 less , in order to calculate this you have to change the mixed fraction to a normal one
15 / 8 * 3= 5,625 so that´s the equivalent to what he takes in running 3/8
so now we reduct that from the 15 seconds and you´ll have the answer
  15,000
-  5,625

 9,375

so that´s it i hope i helped you

Hello!
volume of sphere =4/3.pi.r^3