Here's why:

* Longitude lines circle the Earth from North Pole to South Pole.

* East longitude is measured east of the Prime Meridian (0 degrees longitude).

* 172° East is a very eastern longitude, putting it in the middle of the Pacific Ocean.

To be more specific:

* 172° East passes through the Pacific Ocean, south of the Solomon Islands, north of New Zealand, and east of Fiji.

If you'd like a visual, you can use a map or online mapping tool to find the line of 172° East longitude.