@Randy Dandy,
Let velocity of shot A be vA
Let velocity of shot B be vB
Let velocity of shot C be vC
Let time of shot A to reach target A be tA
Let time of shot B to reach target B be tB
Let time of shot C to reach target C be tC
We know vA is 3/5 miles divided by 3 secs
3/5 divided by 3 is 1/5
vA is 1/5 miles per second
so...
vB is to vA as 5 is to 6
vB is 5/6 times 1/5 miles per second
5/6 x 1/5 = 5/30 = 1/6
vB is 1/6 miles per second
tB is 1 divided by 1/6
tB = 6 seconds
vC is to vA as 4 is to 6
vC is 4/6 times 1/5 miles per second
4/6 x 1/5 = 4/30 = 2/15
tC is 2 divided by 2/15
tC is 15 seconds