the photo attached is the answer for this question DESIGN  AN 8 BIT BCD ADDER CIRCUIT CAPABLE OF ADDING BCD EQUIVALENTS OF TWO DIGIT DECIMAL NUMBERS. INDICATE IC TYPE NUMBERS USED IF THE DESIGN HAS TO BE TTL LOGIC FAMILY COMPATIBLE. i still cant understand it. Can you please give a thourough explanation for it.

8-bit BCD adder. B3 82 81 B0 A3A2 A Ao Cin 4- Bit Binary adder Cinuo 4- Bit Binary adder 3 210 Cout Cout Cin=0 4- Bit Binary adder Cinmo 4- Bit Binary adder (Ignored) (Ignored) Digit 2 Digit 1 Digit 0