Keri has an e$-$tail poster business. Suppose Keri expects to sell $2,400$ posters. Her average sales price per poster is $$30$ and her average cost per poster is $$27.$ Her fixed expenses total $$1,560.$ Compute her margin of safety

a$.$ in units $($posters$).$

b$.$ in sales dollars.

c$.$ as a percentage of expected sales.

a$.$ Begin by determining the formula, then compute the margin of safety in units $($posters$).$

$-1=$ Margin $of$ safety $in$ units