Answer:
252 is the answer
Explanation:
find the multiples of all of them ( and make sure it is the least. )
28:
28, 56, 84, 112, 140, 168, 196, 224, 252, 280, 308
42:
42, 84, 126, 168, 210, 252, 294, 336
63:
63, 126, 189, 252, 315, 378
bolded + undurlined is the answer
you see that 252 is the answer
252 is the answer