how to find the payback period

[The following information applies to the questions displayed below.J Beacon Company is considering automating its production facility. The initial investment in automation would be $10.22 million, and the equipment has a useful life of 8 years with a residual value of $1,100,000. The company will use straight-line depreciation. Beacon could expect a production increase of 40,000 units per year and a reduction of 20 percent in the labor cost per unit. Current (no automation) 77,000 units Proposed (automation) 117,000 units Production and sales volume Per Unit $ 92 Per Unit $ 92 Total Sales revenue Variable costs Direct materials Direct labor Variable manufacturing overhead 17 30 10 57 $35 $ 17 10 41 Total variable manufacturing costs Contribution margin Fixed manufacturing costs $1200,000 $ 2180,000 Net operating income 110:1