Any number smaller than 49 goes into 49. Any number smaller than 42 goes into 42. And any number smaller than 21 goes into 21.
But if you want them to go in EVENLY, with no remainder, then you're looking for the FACTORS of those numbers.
The factors of 49 are 1, 7, and 49 .
The factors of 42 are 1, 2, 3, 6, 7, 14, 21, and 42 .
The factors of 21 are 1, 3, 7, and 21 .
The COMMON factors of 49, 42, and 21 ... the numbers that go into ALL of them evenly ... are 1 and 7 .
( 1 is a factor of EVERY whole number.)