Final answer:
The penalty for making a stroke at an incorrectly substituted ball in golf is two strokes, with an additional two-stroke penalty if the mistake is not corrected.
Step-by-step explanation:
According to the Rules of Golf, if a player makes a stroke at an incorrectly substituted ball, the penalty is two strokes. The player must then correct the mistake by playing the ball that was supposed to be substituted, without penalty. If the mistake is not corrected, an additional two-stroke penalty is added to the player's score.