Note: A BCD number $($Binary Coded Decimal$)$ can go only from $0$ to $9.$ If you go past $9,$ that will be an invalid BCD code and is not supposed to happen. You need at least $4$ bits to code a decimal digits $($there are $10$ of them$).$ But with $4$ bits, you can have $16$ binary numbers. So $16-10=6$ of them are invalid. So the last $6$ rows in the truth table are invalid and therefore their outputs will be don't care.

$\backslash$table$[[$w$,x,y,z,b_0,b_1,b_2,b_3,b_4,b_5,b_6$