Wich one of these numbers is not like the others 21,15,6,16,27

An energy plant is looking into putting in a system to remove harmful pollutants from its emissions going into earth's atmosphere. the cost of removing the pollutants can be modeled using the function c = 25000p/100 -p what is the vertical asymptote?

Sam claims that cos x =sin y if x and y are congruent angels. is sam correct ?

Solve: 3x+y=6 4x-2y=18 show all work !