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
);
    assign sum=a^b^cin;
    assign cout=(a&b)|(a&cin)|(b&cin);

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 w0,w1,w2,w3;
    wire q0,q1,q2,q3;

    full_adder_1bit fa0(
        .a(a[0]),
        .b(b[0]),
        .cin(cin),
        .sum(q0),
        .cout(w0)
        );
    full_adder_1bit fa1(
        .a(a[1]),
        .b(b[1]),
        .cin(w0),
        .sum(q1),
        .cout(w1)
        );
    full_adder_1bit fa2(
        .a(a[2]),
        .b(b[2]),
        .cin(w1),
        .sum(q2),
        .cout(w2)
        );
    full_adder_1bit fa3(
        .a(a[3]),
        .b(b[3]),
        .cin(w2),
        .sum(q3),
        .cout(w3)
        );
        assign sum={q3,q2,q1,q0};
        assign cout=w3;
endmodule