$1\mathrm{.}5.$ Semi$-$Variable Costs The Lakeshore Hotel$$s guest$-$days of occupancy and custodial supplies expense over the last seven months were: Month Guest$-$Days of Occupancy Custodial Supplies Expense March $4,000$ Rs$7,500$ April $6,500$ Rs$8,250$ May $8,000$ Rs$10,500$ June $10,500$ Rs$12,000$ July $12,000$ Rs$13,500$ August $9,000$ Rs$10,750$ September $7,500$ Rs$9,750$ Guest$-$days is a measure of the overall activity at the hotel. For example, a guest who stays at the hotel for three days is counted as three guest$-$days. Required: $1.$ Using the high$-$low method, estimate a cost formula for custodial supplies expense. $2.$ Using the cost formula you derived, above, what amount of custodial supplies expense would you expect to be incurred at an occupancy level of $11,000$ guest$-$days?