public async Task <Order> Calc(Order order) { decimal totalTax = await taxCalculator.CalcTaxAsyn(order); decimal total = 0; if (order.Items.Count > 0) { total = order.Items.Select(a => a.Price * a.Quantity).Sum(); } total += totalTax; order.Total = total; order.TotaTax = totalTax; return(order); }