jason charges $$30$ to clean the main areas of an apartment. in addition to his equipment costs, he uses a cleaning solution on the carpet, which costs about $$3$ per unit cleaned. beacuse of his class load, jason currently cleans just $4$ apartments per month, but he is thinking about asking his roomate to join him so that he can increase the volume of sales. at his current level of activity, jason's degree of operating leverage is $1\mathrm{.}5.$ how much are his monthly fixed costs?