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