Sarah has an online poster business. Suppose Sarah expects to sell 1,000 posters. Her average sales price

Question:

Sarah has an online poster business. Suppose Sarah expects to sell 1,000 posters. Her average sales price per poster is $31 and her average cost per poster is $21. Her fixed expenses total $6,000. Compute her margin of safety
a. In units (posters).
b. In sales dollars.
c. As a percentage of expected sales.