Transact SQL :: How To Select Number For Varchar Column

I have a table with number and varchar columns. The last insert statement has 1 inserted.

The  select statement should retrieve    

a          b                                                          
1         1

CREATE TABLE [dbo].[test1](
 [a] [int] NULL,
 [b] [varchar](10) NULL
) ON [PRIMARY]
  insert into test1 values (1,'a')
  insert into test1 values (2,'b')
  insert into test1 values (4,'d')
  insert into test1 values (12,'x')
  insert into test1 values (15,NULL)
  insert into test1 values (1,1)