42/4 can be reduced by dividing numerator and denominator by 2: 21/2.
This is an improper fraction. One way to obtain the equivalent mixed number would be to multiply numerator and denominator of 21/2 by 5, obtaining 105/10, which reuces to 10.5.
We could also divide 42 by 4 in the usual way, obtaining 10.5.
