All multiples of 840 are common multiples of 60 and 280
840
840
Any multiple of 4200
Any multiple of 840.
420, 840, 1260 and so on.
210, 420, 630, 840 . . .
280, 560, 840
420, 840, 1260
840, 1680, 2520
420, 840, 1260 and so on.
The common multiples of 4, 5, 7, and 15 are 420, 840, 1260 and so on.