Let Y = total costs, X1 = production volume, and X2 = number of setups. Which of ~e following are linear cost functions? Which are mixed cost functions?

a. Y = $8X1

b. y = $1,500

c. Y = $8,500 + $ I.50X1

d. Y = $3,000 + $6X1 + $30X2

e. Y = $9,000 + $3(X1 X X2)

f. Y = $5,000 + $4.00X1