A certain section of a forest is undergoing a pine-beetle infestation. A biologist has determined that the number of pine-beetle infected trees fluctuates from acre to acre, with an average of $9.6$ pine-beetle infected trees per acre.
a) What is the probability that between $7$ and $9$, inclusive infected trees are found?
b) What is the probability that more than $12$ pine beetle infected trees are found?
c)As a way to combat the infestation, the infected trees are to be sprayed with an insecticide at a cost of $5$ $dollars$ for every tree infested with pine beetle(s), plus an overhead fixed cost of $70$ $dollars$ for equipment rental. Letting Cost represent the total cost for spraying all the pine-beetle infested trees for a randomly chosen acre of forest. Find the expected cost of spraying an acre. In addition, find the standard deviation in the cost of spraying an acre.
I'm pretty sure this is a normal distribution centered around the average value of 9.6, but using a normal distribution calculator, I'm not getting the correct answers.