The income statement for Windsor Manufacturing Company for 2023 is as follows: Sales (10,000 $120,000 units) Variable 72,000 expenses Contribution $ 48,000 margin Fixed 36,000 expenses Operating $ 12,000 income If sales increase by 1,000 units, what will happen to pre-tax operating income? O stays the same increase by $7,200 increase by $720 O increase by $4,800 increase by $1,200