The binary$-$coded$-$decimal $($BCD$)$ format uses $4$ bits to represent $10$ decimal digits. Design a BCD adder

system, that will take two BCD digits as input and the output will also be in BCD format. For example,

if two input BCD digits are $7$ and $8$ then the output will be $15$ but in BCD it might look like,

$00010101.$