NoMethodError: undefined method `expenses'

I am trying to figure out why I am receiving the following error. I am
following an Apple Developers Rail Application tutorial.

event.expenses.create(:vendor => vendor1, :amount =>75.00)

NameError: undefined local variable or method `vendor1' for
  from (irb):2

Here is what I have for the models

class Event < ActiveRecord::Base
  validates_presence_of :name
  validates_numericality_of :budget, :greater_than => 0.0

  has_many :expenses
  has_many :vendors, :through => :expenses

UMQ: Use More Quotes!

:vendor => "vendor1", :amount => "75.00"

Link? The reason is you're using a temporary variable you haven't set
to any value before you're using it. You probably want a string
'vendor1' rather than vendor1 which is a temp variable.