added tax.rb
added tax method to Imported class
added Exempt class
added Goods superclass and fixed multiple methods
changed rover.new's starting point
changed rover.new starting point
renamed tax.rb to tax.classes.rb
deleted tax.rb
made tax classes.rb
made tax receipt.rb
added cost method to Goods superclass
fixed initailize paramater and instance variable problem
removed cost method and moved it to tax receipt.rb
added cost method out of Goods superclass
removed cost method to troubleshoot
fixed cost nil class problem
fixed nil price error
fixed classes and cost results
add name instance variable and edited receipt method