Help me what is D please help ASAP

Which of the following is most likely the next step in the series? a3z, b6y, c9x, d12w, е15v, f18u

Colby and jaquan are growing bacteria in an experiment in a laboratory. colby starts with 50 bacteria in his culture and the number of bacteria doubles every 2 hours. jaquan starts with 80 of a different type of bacteria that doubles every 3 hours. let x equal number of days. colbys experiment follows the model: a.) y=50*2^x b.) y=50*2^8x c.) y=50*2^12x jaquans experiment follows the model: a.)80*2^x b.)80*2^8x c.)80*2^12x

Apositive number a or the same number a increased by 50% and then decreased by 50% of the result?