The factors of 42 are 1, 2, 3, 6, 7, 14, 21, 42. The way to calculate the factors of 42 is as follows. First, every number is divisible by itself and 1.
Try 1. 1 x 42 = 42, so put these into our factor list.
1
...
42
Take 2. 2 x 21 = 42, which means we add these to our factor list.
1
2
...
21
42
Now take 3. 3 x 14 = 42, so now we put these in our list of factors.
1
2
3
...
14
21
42
Next try 4... no luck. 42/4 isn't a whole number. So we skip 4.
Now try 5... nope! 42/5 isn't a whole number. So we skip 5.
Try 6. 6 x 7 = 42, which means we add these to our factor list.
1
2
3
6
...
7
14
21
42
Now, since we don't have any more numbers to try, we're done!