65. Ripple Carry Adder

How do you plan to solve it?

// 1-bit Full Adder (to be used by the 4-bit RCA)
module full_adder_1bit (
    input  a, b, cin,
    output sum, cout
);
wire s1, s2, s3;
    xor (s1, a, b);
    xor (sum, s1, cin);
    and (s2, a, b);
    and (s3, s1, cin);
    or (cout, s2, s3);
    
endmodule

// 4-bit Ripple Carry Adder – chain 4 full adders
module rca4_chain (
    input  [3:0] a,
    input  [3:0] b,
    input        cin,
    output [3:0] sum,
    output       cout
);
 wire c1, c2, c3;

    full_adder_1bit d0 (a[0], b[0], cin, sum[0], c1);
    full_adder_1bit d1 (a[1], b[1], c1, sum[1], c2);
    full_adder_1bit d2 (a[2], b[2], c2, sum[2], c3);
    full_adder_1bit d3 (a[3], b[3], c3, sum[3], cout);

endmodule