Basic Math in Ruby on Rails -

this question simple should embarrassed ask, searches answers came structuring complex math expressions in ror - need on far more basic.

i have rails 4 app creating invoices. each line_item has price, units, , tax. need multiply price units, multiply times tax if taxable boolean true , add come total.

where i'm struggling figuring out how structure these calculations , equally important, place them in code saves db. inclination put them in model, i'm unsure of.

my attempt @ doing myself adding basic function controller:

def create @line_item = lineitem.new(line_item_params) @line_item.invoice_id = @invoice @line_item.total = @line_item.price * @line_item.units  respond_to |format|   if @line_item.save     format.html { redirect_to @line_item, notice: 'line item created.' }     format.json { render :show, status: :created, location: @line_item }   else     format.html { render :new }     format.json { render json: @line_item.errors, status: :unprocessable_entity }   end end 

end

if can show me example, or resources discuss basic math in ruby, i'd appreciate greatly.

i'm not ror developer, think doing these calculations on front-end easier.

other that, these resources found possibly useful:

• http://docs.railsbridge.org/ruby/numbers_and_arithmetic
• https://www.tutorialspoint.com/ruby-on-rails/rails-maths-functions.htm
• doing basic math in rails within each "each do" loop , getting sum