Answer
Sheridan should buy because doing so would save it $5900
Step-by-step explanation
To determine the right course of action we will consider the relevant cost of making and buying
The relevant cost of making $
Variable cost ( 18 × 5,900 106200
Fixed cost (3× 5,900) 17700
Total cost 123,900
Relevant of buying (20 × 5,900 ) = 118,000
Saving in cost by buying = 123,900 -118,000 =$5900