Which counterexample can be used to show that the following conjecture is false?

Autility company burns coal to generate electricity. the cost c(p), (in dollars) of removing p percent of the some stack pollutants is given by c(p)= 85000p/100-p a) find the cost to remove 30% of the pollutant b) find where the function is undefined

Can someone me and explain..will award brainlest!

Compute the standard deviation of the following set of data to the nearest whole number. 10, 10, 15, 20, 25