In `Javascript`, I have 4 variables with values. 

Below are the examples :

```
var start_hour = 1;
var start_minute = 00;
var end_hour = 6;
var end_minute = 30;

```

I want to create a javascript function that can calculate duration and print like for above example, the duration output should be `5:30` means, `5 Hours & 30 Minutes`.