What is the answer to -2ab +ab+ 9ab-3ab

If the measure of xyz is 81 what is the measure of yz

Acircle has a radius of 5/6 units and is centered at (3.6, 7.8) write the equation of this circle

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.