If I had box 12a on my W-2 form,with a code C and an amount of 674.28,what do I enter on my tax return?

[PaulaM]

Box 12 with a code c is the taxable cost of group-term insurance over $50,000. If you had group term life insurance through your workplace, the premiums for any value over $50,000 become taxable income to you and are included in box 12.

Enter your W-2 form with the box 12 code C in your tax return. The taxable amount is already included in your Box 1 wages. You don't enter the amount anywhere else in your return.

https://ttlc.intuit.com/questions/1899457-what-do-the-letter-codes-in-box-12-of-my-w-2-mean