$3$a$.$ Calculate the unit sales per month at which Frieden management will be indifferent between doing the major upgrade to the manufacturing equipment and not doing the upgrade.

$3$b$.$ Based on the above analysis, should Friedan proceed with the major upgrade? Yes or No$.$

$3$c$.$ Why or why not?

In this case, the indifference point would be $\_\_\_\_\_\_$ at the current level of sales at which the upgrade $\_\_\_\_\_$ have an impact on the operating income. So Frieden's $\_\_\_\_\_$ proceed to upgrade.

$4$a$.$ Refer to the orginal data. Instead of doing the major upgrade to the equipent, management is considering introducing a new advertising campaign that will increase fixed expenses by $$25,000$ per month. Management believes the new advertisements will increase monthly unit sales by $10\%.$ In this case, what would be impact on operating income.