Tammy's Nursery sells maple trees to landscapers for $$30$ each. During the year $2022,$ Tammy sold $500$ maple trees and had total fixed costs of $$7,000.$ Tammy's contribution margin ratio for the year was $0\mathrm{.}8.$

$10.$ What was Tammy's variable cost per tree during $2022?$

a$.$ $$24$

b$.$ $$4$

c$.$ $$18$

d$.$ $$6$

$11.$ What amount of total sales dollars would have given Tammy operating income before tax of $$5,000$ for the year $2022?$

a$.$ $$15,000$

b$.$ $$6,250$

c$.$ $$12,500$

d$.$ $$20,000$

$12.$ A firm is trying to decide whether to keep an old machine that has no salvage value or buy a new one that will perform similar tasks. Which of the following costs is irrelevant to making this decision?

a$.$ Original cost of the old machine

b$.$ Cost to purchase the new machine

c$.$ Difference in operating costs for the two machines

d$.$ Cost of training workers to use the new machine