Edit in JSFiddle

var viewModel = {};
viewModel.Product = ko.observable(null);
viewModel.Products = [ "Satin Pyjamas", "Jeans", "Leather Wallet" ];
viewModel.GiftWrap = ko.observable("No");
viewModel.Greating = ko.observable("");
viewModel.Delivery = ko.observable("Kharkov");
viewModel.Address = ko.observable("");
viewModel.Carrier = ko.observable(null);
viewModel.Carriers = ["Autolux", "International", "Express"];

viewModel.Summary = ko.dependentObservable(
    function(){
        var summary = "";
        summary += this.Product();
        summary += (this.GiftWrap() == 'Yes') ? " in gift wrap" : " in simple wrap";
        summary += (this.GiftWrap() == 'Yes' && this.Greating() != '') ? (" with greating '" + this.Greating() + "'") : "";
        summary += "<br />";
        summary += "Delivery address: " + this.Address();
        summary += (this.Delivery() == 'Ukraine') ? " with " + this.Carrier() + " carrier" : "";
        summary += "<br />";
        return summary;
    },
    viewModel);

viewModel.Total = ko.dependentObservable(
    function() {
        var total = 0;
        total += (this.GiftWrap() == 'Yes') ? 20 : 5;
        
        if (this.Delivery() == 'Kharkov'){
            total += 30;
        } else {
            if (this.Carrier() == 'Autolux'){
                total += 20;
            }
            
            if (this.Carrier() == 'International'){
                total += 10;
            }
            
            if (this.Carrier() == 'Express'){
                total += 35;
            }
        }
        
        return total;
    },
   viewModel);

ko.applyBindings(viewModel, document.getElementById("koSample"));

<div id="koSample">
    <div>
        <label>Product</label>
        <select data-bind="options: Products, value: Product">        
        </select>
    </div>
    <div>
        <label>Gift Wrap</label>
        <input type="radio" name="wrap" value="Yes" data-bind="checked: GiftWrap" /> Yes
        <input type="radio" name="wrap" value="No" data-bind="checked: GiftWrap" /> No
    </div>
    <div data-bind="visible: GiftWrap() == 'Yes'">
        <label>Greating</label>
        <input type="text" data-bind="value: Greating, valueUpdate: 'keyup'" />    
    </div>
    <div>
        <label>Delivery</label>
        <input type="radio" name="delivery" value="Kharkov" data-bind="checked: Delivery" /> Kharkov
        <input type="radio" name="delivery" value="Ukraine" data-bind="checked: Delivery" /> Ukraine
    </div>
    <div>
        <label>Address</label>
        <input type="text" data-bind="value: Address" />            
    </div>
    <div data-bind="visible: Delivery() == 'Ukraine'">
        <label>Carrier</label>
        <select data-bind="options: Carriers, value: Carrier">        
        </select>
    </div>
    <div>
        Summary 
        <p>
            <span data-bind="html: Summary"></span><br />
            <div id="total">Total: $<span data-bind="text: Total"></span></div>
        </p>
    </div>
</div>