This is from Microsoft Visual C#: An Introduction to Object-Oriented Programming Exercise 9-4

Create a program named PaintingDemo that instantiates an array of eight Room objects and demonstrates the Room methods. The Room constructor requires parameters for length, width, and height fields (all of type int); use a variety of values when constructing the objects. The Room class also contains the following fields: Area - The wall area of the Room (as an int) Gallons - The number of gallons of paint needed to paint the room (as an int) Both of these values are computed by calling private methods. Include read-only properties to get a Rooms values. A room is assumed to have four walls, and you do not need to allow for windows and doors, and you do not need to allow for painting the ceiling. A room requires one gallon of paint for every 350 square feet (plus an extra gallon for any square feet greater than 350). In other words, a 12 x 3 x 10 room with 9-foot ceilings has 396 square feet of wall space, and so requires two gallons of paint.

I want to make sure this error does not appear when using Chegg:

NtTest0bc704fa.cs(12,5): error CS0246: The type or namespace name `Room' could not be found. Are you missing `PaintingDemo' using directive? NtTest0bc704fa.cs(13,26): error CS0841: A local variable `room1' cannot be used before it is declared NtTest0bc704fa.cs(15,5): error CS0246: The type or namespace name `Room' could not be found. Are you missing `PaintingDemo' using directive? NtTest0bc704fa.cs(16,26): error CS0841: A local variable `room2' cannot be used before it is declared NtTest0bc704fa.cs(18,5): error CS0246: The type or namespace name `Room' could not be found. Are you missing `PaintingDemo' using directive? NtTest0bc704fa.cs(19,26): error CS0841: A local variable `room3' cannot be used before it is declared