Final answer:
The student should insert two commas around 'Mr. Shelton' in the given sentence.
Step-by-step explanation:
Correcting punctuation in a sentence involves ensuring that the appropriate punctuation marks are used in the right places to convey meaning accurately and clearly. Punctuation is a set of symbols that help structure and organize written language. Commas should be placed around 'Mr. Shelton' in the given sentence. The corrected sentence will be: 'If you think you can fix my car, Mr. Shelton, I won't take it to a mechanic.'