For Challenge 1 for the pistols take your time and hit the middle of the target on all of the targets. You have plenty of time to do this.
For Challenge 2 for the pistols the targets drop down and move along. Use the third pistol in the weapon selection, since this pistol is automatic. Hold down the trigger and aim at the middle of the target. Immediately change targets when a new one pops up so you don’t miss the target when it automatically disappears which would mean your combo resets.
For Challenge 3 for the pistols also use the automatic pistol. The target starts on the right of the screen and moves to the left. Keep your aim on the middle of the target and hold down the trigger. If you can keep the multiplier throughout this challenge you will get gold.