Heat Man Screen 1

Most of this screen is trivial - hold right and shoot enemies.

The Item 3 Throw Section

Switch to item 3 after walking off the high platform. Pause and switch to item 3 here - pausing itself (even without switching weapons) resets the falling speed so you reach the lower platform.

The item 3 throw is rather precise. The backup is to instead switch to item 2, or just platform normally.