Answer:
Step-by-step explanation:
Expression that defines a growth function is,

Here,
initial amount
growth rate
And
= Growth factor
Similarly, decay function is represented by the expression,

That means if a function has a growth factor (1 + r) or greater than 1, function will have a exponential growth.
And a function with growth factor between 0 to 1, it will be a decay.
1). 

Growth rate = 18%
Here, 1.18 > 1
Therefore, function is a growth function.
2). 




Decay rate = 50%
Here growth factor (0.5) is less than 1.
Therefore, function is a decay function.
3). 




Growth rate = 1.7%
Growth factor (1.19) is greater than 1.
Therefore, function will be a growth function.
4). 


Decay rate = 87%
Growth factor (0.13) < 1
Therefore, function will be a decay function.