The jet travels a distance of
(960 km/h) t
after time t, while the light plane travels a distance of
(560 km/h) t
The jet is faster than the light plane, so the distance between them is
(960 km/h) t - (560 km/h) t = (400 km/h) t
so the time it takes for them to be 4560 km apart is
(400 km/h) t = 4560 km
==> t = (4560 km) / (400 km/h)
==> t = 11.4 h