Why might a grocery store engage in cost-plus pricing, while a tire manufacturer relies on equating MR with MC?

Why might a grocery store engage in cost-plus pricing, while a tire manufacturer relies on equating marginal revenue with marginal cost? |||I have no idea what that means. You're doing a course on business aren't you? This is an essay question isn't it?Best way to learn business is to open one up and then deal with the first customer who walks through the door, good steep learning curve