There are cars in the CMC parking lot, which are all Acuras, Beetles, or Camrys. There are half as many Acuras as Beetles. The number of Camrys is %80 of the number of Acuras and Beetles together. How many of the 81 cars are Beetles?
b + 1/2 b + .8(b + 1/2b) = 81
b = 30