Assume that the $10-$mile march has step$-$fixed rather than fixed costs. What does this mean for application of the break$-$even forumula to find the break$-$even number of marchers? a$)$ The break$-$even formula applies the same to step$-$fixed, and fixed costs, b$)$The break$-$even formula will only apply if the number of marchers is in range within which costs are fixed, c$)$ The break$-$even formula cannot be applied in this cirucumstance, d$)$ Whether the break$-$even formula can be applied depends on the structure of the marginal revenue function$-$