I really just need a simple STEP-BY-STEP explanation on how you do percentages.

Well maybe give me some options. But the statements that are true about decay functions are exponential decay are; the domain is all real numbers, the base must be less than 1 and greater than 0 and the function has a constant multiplicative rate of change. The answers are letters A, D and E. An example is when there are 70000 bacteria present in a culture and reduced by half every four hours, the number of bacteria will decrease. The bacteria will experience an exponential decay because it decreases its number at a constant decay. 

Hope it helps!