Answer:
Part 1) 
Part 2) 
Part 3) 
Step-by-step explanation:
we know that
The equation of a exponential growth is equal to

where
a is the initial value
r is the rate of change
Part 1) we have
A scientist initially had 15 micrograms of bacteria in a petri dish, which increased at a rate of 6% each hour
Let
x ---> the number of hours
y ---> micrograms of bacteria
we have

substitute


Convert to function notation

Part 2) we have
The membership price for an online retailer was initially $60 per year, but it increased at a rate of 1.5% per year
Let
x ---> the number of years
y ---> the membership price for an online retailer
we have

substitute


Convert to function notation

Part 3) we have
An online blog started with 150 followers, and the number of followers increased at a rate of 60% each month.
Let
x ---> the number of months
y ---> the number of followers
we have

substitute


Convert to function notation
