contribution margin, accounting homework help

What is unit contribution margin? How is it used in computing the unit breakeven point? What is contribution margin ratio and when is it most useful? How is the breakeven equation modified to take into account the sales required to earn a target profit?

Suppose two companies are the same except that company A has more variable costs than fixed costs. Company B has more fixed costs than variable costs. When sales increase, which company will realize the greatest increase in prof