how to solve second part? what is the formula and how 1160 comes from?

b) If the company's current monthly sales amount is $138,000, what is the margin of safety in dollars and in units? Margin of safety (units) 868 137 138 Part V Margin of Safety 139 140 Biotech Wiring Inc, manufactures one type of computer speaker. The average selling price is $119 per computer 141 speaker. The average variable cost amounts to $47 per computer speaker. The company's fixed costs are $21,000 per 142 month. 143 144 Required: 145 146 a) Calculate the monthly volume sales needed to break-even. 147 148 Break Even Point (Units) 292 149 154 155 b) if the company's current monthly sales amount is $138,000, what is the margin of safety in dollars and in units? 156 158 Margin of safety (units) 868 159 16