Rates are usually written in unit because it shows you the amount of something per one of the thing it is being compared to (EX: 5 oz/ 1 pig)
Answer:

Step-by-step explanation:
we know that
The equation of a exponential growth function is equal to

where
y is the average annual salary
x is the number of years
r is the rate of change
a is the initial value
In this problem we have

substitute


For x=4 years

<span>(4ab^3)(-5b^6)(2a^2)
= (5 * -4 * 2)(a * a^2)(b^3 * b^6)
= -40a^3b^9
hope it helps</span>