Getting Next Transaction Number

My Transaction_ID (varchar) contains following pattern

DXB1
DXB2
.....
DXB15
...
DXB200

The next transaction_id would be DXB201, How to get that one from SQL Query

I am using

SELECT  MAX(transaction_id) AS Expr1
FROM    transaction_master
WHERE   (transaction_id LIKE 'DXB%')

but it fails to give correct output after i.e. query returns DXB9 even though DXB15 is present