Please provide explanation. Thank you

Make or Buy (or Lease) A company can manufacture a part for $25 per unit, which includes $21 of variable cost and $4 of fixed cost (plant building straight-line depreciation). If the part is purchased, the plant space freed up will remain idle. The part can be purchased for $22 per unit. Should the company make or buy and what is the monetary advantage per unit of following your choice. Buy for a savings of $3 per unit Buy for a savings of $1 per unit Make for a savings of $3 per unit Make for a savings of $1 per unit O Make for a savings of $4 per unit