The cost to produce Part A was $12 per unit in 2019. During 2020, it has increased to $15 per unit. In 2020, Sandhill Company has offered to supply Part A for $11 per unit. For the make-or-buy decision:

a) incremental revenues are $4 per unit.

b) net relevant costs are $3 per unit.

c) differential costs are $4 per unit.

d) incremental costs are $3 per unit.

Jenny​ walters, who owns a real estate​ agency, bought an old house to use as her business office. she found that the ceiling was poorly insulated and that the heat loss could be cut significantly if six inches of foam insulation were installed. she estimated that with the​ insulation, she could cut the heating bill by​ $80 per month and the​ air-conditioning cost by​ $70 per month. assuming that the summer season is three months​ (june, july, and​ august) of the year and that the winter season is another three months​ (december, january, and​ february) of the​ year, how much can jenny spend on insulation if she expects to keep the property for five​ years? assume that neither heating nor​ air-conditioning would be required during the fall and spring seasons. if she decides to install the​ insulation, it will be done at the beginning of may.​ jenny's interest rate is​ 6% compounded monthly.