Conversion from Decimal form to BCD
If we want to represent 8 base 10 then it will be represented as follows:

A) 7421 code
   8(10)= 7+1 = 8        
   1 0 0 1 -&gt; 7 4 2 1 code
   1x7+4x0+2x0+1x1=7+0+0+1=8
   8(10)=1001(7421)

B) 5421 code
   8(10)= 5+2+1 
   therefore   5 4 2 1
               1 0 1 1
  8(10)= 1011(5421)

C) 4221 code
   8(10)= 4+2+2
   therefore 4 2 2 1
             1 1 1 0
   8(10)= 1110(4221)


There you go. If this is helpful then please select this as an answer.