A $66-$kg student eats a $575-$Calorie $(575$ kcal $)$ jelly doughnut for breakfast.

$($a$)$ How many joules of energy are the equivalent of one jelly doughnut?

$\_\_\_\_$ J

$($b$)$ How many stairs must the woman climb to perform an amount of mechanical work equivalent to the food energy in one jelly doughnut? Assume the height of a single stair is $15$ cm $.$

$\_\_\_\_$stairs

$($c$)$ If the human body is only $28\%$ efficient in converting chemical energy to mechanical energy, how many stairs must the woman climb to work off her breakfast?

$\_\_\_$stairs