What Index should i create for N1QL rest API?

I am using following query statement for N1QL public Rest API. I have seen there was some delay. So what type of Index i should create and what is the syntax for that. Please assist me.

My N1QL query is…

SELECT firstName, lastName, number, FROM students WHERE type=‘studentdetails’ AND department = ‘3’ AND collegeID = ‘101’ ORDER BY number OFFSET 0 LIMIT 50

CREATE INDEX ix1 ON students(collegeID, department,  number, firstName,lastName) 
WHERE type = "studentdetails";


Thank you, i will check it.