calculating values after rendering page in rails

Hi all.. I am trying to generate a report which has multiple columns.. After rendering the report I allow the user to enter a value which is to be subtracted from the column which is already rendered.. I have multiple rows.. so I have tries like the following. My views page is

<script>   function sum() {   var txtFirstNumberValue = document.getElementById('txt1').value;   var txtSecondNumberValue = document.getElementById('txt2').value;   var result = parseFloat(txtFirstNumberValue) - parseFloat(txtSecondNumberValue);    if(!isNaN(result)) {    document.getElementById('txt3').value = result; } } </script> <% @arr.each do |j| %> <% @q = %> <% t= 0 %> <%= form_for ProductionReport.new ,:url=>{:controller=>"users",:action=>"rate_per_unit_report" } do |i| %> <tr> <td><%= j[0] %></td> <td><%= j[1] %></td> <td><%= j[2] %></td> <% @q << j[3] %> <td><%= i.text_field j[3], :value=>@q[t], :id=>"txt1", :onkeyup=>"sum()", :class=>"txt" %></td> <td><%= i.text_field :selling_price, :id=>"txt2", :onkeyup=>"sum()", :class=>"txt" %></td> <td><%= i.text_field :profit_loss, :id=>"txt3", :class=>"txt", :readonly =>true %></td> <% end %> <% t = t+1 %> <% end %> <td>total</td> <td><%= @total %></td> <td><%= @total1 %></td> <td><%= @total2 %></td>

My controller is

def rate_per_unit_report   @user=User.new   @user = User.find(session[:user_id]).name   @rpus = params[:production_report][:intial_date]   @rpue = params[:production_report][:final_date]   @production_report = ProductionReport.where(:date => @rpus..@rpue)   @production = @production_report.select(:finished_goods_name).uniq   @arr=   g = 0   @production.each do|i|     @p = @production_report.pluck(:issue_id)     @ll = @production_report.where(:finished_goods_name=>i.finished_goods_name).select(:total_no_of_items_produced).sum :total_no_of_items_produced     @k = Issue.where(:id=>@p).pluck(:consolidated_cost)     @rate = @k[g].to_f / @ll.to_f     @r = @rate.round(2)     @arr<<[i.finished_goods_name]+[@ll]+ [@k[g]] + [@r]     g = g+1   end   @total=@arr.inject(0){|sum,x| sum + x[1].to_i }   @total1=@arr.inject(0){|sum,y| sum + y[2].to_i }   @total2=@arr.inject(0){|sum,z| sum + z[3].to_i } end

And my sample output page is attached as an image.. Pls look at it..

Shortly., I need to dynamically compute profit/loss based on the selling price entered by the user. How could I achieve that.. Kindly pls help me.. Thanks in advance..

Attachments: http://www.ruby-forum.com/attachment/11304/rateperunit.png http://www.ruby-forum.com/attachment/11305/rateperunit.jpg