Can you please help with these four, not getting the concept. Thanks

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variable costs as a percentage of sales for Lemon Inc. are 77%, current sales are $655,000, and fixed costs are $181,000. How much will operating income change if sales increase by $36,900? Ca. $8,487 increase Ob. $8,487 decrease Oc, $28,413 decrease Od. $28,413 increase