The cost structure of Dennis's Retail Mart is dominated by variable costs with a contribution margin ratio of $0\mathrm{.}31$ and fixed costs of $$72,120.$ Every dollar of sales contributes $31$ cents toward fixed costs and profit. The cost structure of a competitor, Oakfield Convenience Store, is dominated by fixed costs with a higher contribution margin ratio of $0\mathrm{.}69$ and fixed costs of $$552,920.$ Every dollar of sales contributes $69$ cents toward fixed costs and profit. Both companies have sales of $$1,202,000$ for the year.

Required:

a$.$ Compare the two companies' cost structures.

b$.$ Suppose that both companies experience a $10$ percent increase in sales volume. By how much would each company's profits increase?