Your firm spends $ $400$ comma $000$ per year in regular maintenance of its equipment. Due to the economic$$ downturn, the firm considers forgoing these maintenance expenses for the next $3$ years. If it does$$ so$,$ it expects it will need to spend $ $1\mathrm{.}9$ million in year $4$ replacing failed equipment.$$

a$.$ What is the IRR of the decision to forgo maintenance of the$$ equipment?

b$.$ Does the IRR rule work for this$$ decision?

c$.$ For what costs of capital$($COC$)$ is forgoing maintenance a good$$ decision?