Plz tell me what that is i dont speak math

Christina can paint 420 square feet in 105 minutes. which unit rate describes the scenario?

An automobile assembly line operation has a scheduled mean completion time, μ, of 12 minutes. the standard deviation of completion times is 1.6 minutes. it is claimed that, under new management, the mean completion time has decreased. to test this claim, a random sample of 33 completion times under new management was taken. the sample had a mean of 11.2 minutes. assume that the population is normally distributed. can we support, at the 0.05 level of significance, the claim that the mean completion time has decreased under new management? assume that the standard deviation of completion times has not changed.

Acd that is originally priced at $15.85 red-tagged for the sale. what is the sale price of the cd