Contoso University - DbContextOptionsBuilder' does not contain a definition for 'UseSqlServer'

I am trying to work through the Contoso University example application.  I have simply copied the Startup.cs class statements:

services.AddDbContext<SchoolContext>(options =>
options.UseSqlServer(Configuration.GetConnectionString("DefaultConnection")));

I receive the error:

DbContextOptionsBuilder' does not contain a definition for 'UseSqlServer' and no accessible extension method. 'UseSqlServer' accepting a first argument of type 'DbContextOptionBuilder' could be found ( are you missing a using directive or an assemply reference)

What do I need to do to move forward?

Thanks