I guess there is no way to paste a database diagram here, so here is my idea:
CREATE TABLE [dbo].[tblClass](
[ClassName] [nchar](10) NULL,
[RoomName] [nchar](10) NULL
) ON [PRIMARY]
GO
ALTER TABLE [dbo].[tblClass] ADD CONSTRAINT [PK_ClassName] PRIMARY KEY CLUSTERED
(
[ClassName] ASC
)GO
CREATE TABLE [dbo].[tblCompany](
[CompanyID] [nchar](10) NULL,
[CompanyName] [nchar](10) NULL
) ON [PRIMARY]
GO
ALTER TABLE [dbo].[tblCompany] ADD CONSTRAINT [PK_CompanyID] PRIMARY KEY CLUSTERED
(
[CompanyID] ASC
)GO
CREATE TABLE [dbo].[tblRooms](
[RoomName] [nchar](10) NULL
) ON [PRIMARY]
GO
ALTER TABLE [dbo].[tblCompany] ADD CONSTRAINT [PK_RoomName] PRIMARY KEY CLUSTERED
(
[RoomName] ASC
)GO
CREATE TABLE [dbo].[tblTeachers](
[CompanyId] [nchar](10) NULL,
[Teacher] [nchar](10) NULL
) ON [PRIMARY]
GO
ALTER TABLE [dbo].[tblTeachers] ADD CONSTRAINT [PK_Teacher] PRIMARY KEY CLUSTERED
(
[Teacher] ASC
)GO
CREATE TABLE [dbo].[tblCompClass](
[CompanyId] [nchar](10) NULL,
[ClassID] [nchar](10) NULL
) ON [PRIMARY]
GO
ALTER TABLE [dbo].tblCompClass] WITH CHECK ADD CONSTRAINT [FK_tblCompClass_Company] FOREIGN KEY([CompanyID])
REFERENCES [dbo].[tblCompany] ([CompanyID])
GO
ALTER TABLE [dbo].[tblCompClass] CHECK CONSTRAINT [FK_tblCompClass_Company]
GO
ALTER TABLE [dbo].[tblCompClass] WITH CHECK ADD CONSTRAINT [FK_tblCompClass_tblClass] FOREIGN KEY([ClassName])
REFERENCES [dbo].[tblClass] ([ClassName])
GO
ALTER TABLE [dbo].[tblCompClass] CHECK CONSTRAINT [FK_tblCompClass_tblClass]
GO
ALTER TABLE [dbo].[tblTeacher] WITH CHECK ADD CONSTRAINT [FK_tblTeacher_tblCompany] FOREIGN KEY([CompanyID])
REFERENCES [dbo].[tblCompany] ([CompanyID])
GO
ALTER TABLE [dbo].[tblTeacher] CHECK CONSTRAINT [FK_tblTeacher_tblCompany]
GO
ALTER TABLE [dbo].[tblClass] WITH CHECK ADD CONSTRAINT [FK_tblClass_tblRooms] FOREIGN KEY([RoomName])
REFERENCES [dbo].[tblRooms] ([RoomName])
GO
ALTER TABLE [dbo].[tblClass] CHECK CONSTRAINT [FK_tblClass_tblRooms]
GO