Between 1/1/2017 and 4/1/2017, what is the average server time of calls under the server DARMON?
between 1/1/2017 and 4/1/2017 refers to Date received between '2017-01-01' and '2017-04-01'; average server time refers to avg(ser_time)
SELECT AVG(CAST(SUBSTR(ser_time, 4, 2) AS REAL)) FROM callcenterlogs WHERE `Date received` BETWEEN '2017-01-01' AND '2017-04-01'