Assuming you have a DbContext (YourDbContext) defined and using the DbContext you can write the queries as below:
using(var dbc = new YourDbContext())
{
var noofstudents= dbc.Students.Select(s => s.StudentId).Count();
var noofclubs = dbc.Clubs.Select(s=>s.ClubId).Count();
var noofhosues =dbc.Houses.Select(s=>s.HouseId).Count();
}
I think your third model class is House not student.
As the ids in each table are primary(assuming), the counts will return the values as you expect.
Also I have used the plural forms of the class as table names, you replace them as they are named in your database.
Hope this will help.