69. Binary Subtractor

How do you plan to solve it?

/*Write your code here*/
module sub4_2c(a,b,diff,bout);
input [3:0]a,b;
output [3:0]diff;
output bout;
wire cout;
assign {cout,diff}={1'b0,a}+{1'b0,(~b)}+5'b00001;
assign bout= ~cout;
endmodule