Question

Question #4d5f3

Answer 1

[Q1] `1` hour
[Q2] The destination is `3` hours behind Sydney.
[Q3] Jakarta, Indonesia

Explanation:

`color(red)"Note: I didn't take the international date line(IDL)"` `color(red)"into consideration. My answer may be wrong."`
If so, I'll be happy to correct the errors.

I assume that the outward and homeward journeys take the same time.
Let `x` the time difference between Sydney and that city.

In the local time at Sydney:
[Outward] Sydney `10` am ⇒ the destination `(2+x)` pm
[Homeward] The destination `(12+x)` pm ⇒ Sydney `10` pm

Then, the outward trip takes `4+x` hours and the homeward trip takes `-2-x` hours.
`4+x=-2-x`
`2x=-6`
`x=-3`

So, it takes `4+(-3)=1` hour from Sydney to that city, and the time at that city is `3` hours behind Sydney.

Note: I didn't take the international date line(IDL) into consideration.

Sydney is situated at about longitude `150` degrees East. So, the destination is at long. `150-15*3=105` degrees East. One of the city at that longitude is Jakarta.
http://latitudelongitude.org/id/jakarta/