add 2 fields containing time values in hh:mm format

[jansson_17]

I have an html web form and am looking for a script which adds the value of 2 fields containing time values in hh:mm format

Example:
Field 1 has a vaule of "1:45"
Field 2 has a value of "1:30"
The desired result should be in a time value "3:15"

Thank You