Answer: Linear model
and H'(t) = 9 units.
Explanation:
Since we have given that
In 2000, amount spent = $100 billions
In 2010, amount spent = $190 billions.
So, rate of increase would be

So, linear model for H(t) would be

So, H'(t) would be 9.
Hence, linear model
and H'(t) = 9 units.