transaction affects the break even volume

For er each of the following please explain how the transaction affects the break even volume (do not just indicate the break even increases or decreases), explain how the transaction affects the contribution margin and the break even volume):
a. The variable cost increased by $.50 per unit and the selling price also increased by $.50.
b. The variable cost increased by $.50 per unit but there was no change to the selling price.
c. At the beginning of the year, rent increased by $600 per month.
d. The variable cost decreased by $.25 per unit but there was no change to the selling price.