I am having trouble finding the contribution margin in per unit. Even though I have the answer I don't understand how they got $6

Menlove Company had the following income statement for the most recent year: Sales (17,000 units).....,,,...... $357,000 Variable expenses 255,000 Contribution margin......m.. 102,000 Fixed expenses ..................... 68,000 Net operating income .......... m Given this data, the unit contribution margin was: A. $2 per unit B. $5 per unit D. $4 per unit