A package will leave Australia on 19 August at 21:15, local time in Australia.
The time taken for the package to arrive at Singapore is 6 hours 30 minutes.
Australia time is 2 hours ahead of that of Singapore time.
What is the date and time at which the package arrives in Singapore?

1. Convert the departure time from Australia time to Singapore time.

Australia time is $2$ hours ahead of Singapore time.

So Singapore time at departure:
$21:15 - 2\text{ h} = 19:15$

The package leaves at $19:15$ on $19$ August in Singapore time.

2. Add the travel time to the Singapore departure time.

Travel time $= 6$ hours $30$ minutes.

$19:15 + 6\text{ h }30\text{ min} = 25:45$

Since $25:45$ is $1$ hour $45$ minutes after midnight, this is $01:45$ on the next day.