I believe the answer is D but i could be wrong. sry for not being absolutely sure.
lol
Answer:
a. Decay
b. 0.5
c. 4
Explanation:
If we have a function of the form

then
a = intital amount
b = growth / decay rate factor
x = time interval
If b > 1; then the equation is modelling growth. If b < 0, then the equation is modelling decay.
Now in our case, we have

Here we see that
inital amount = a = 4
b = 1/ 2 < 0, meaning the function is modeling decay
decay factor = b = 1/2
Therefore, the answers are
a. Decay
b. 0.5
c. 4
Part one of your questions would be 1/20
Part two would be 1/20
Part three. Yes they are equal
Part four. None of them sense there equal