For this case, what we are going to do is first define variables.
x: current number of Americans.
y: number of Americans after the next 15 years.
We now write the expression to model the problem, assuming:
"the rate of increase continues in the same way for the next 15-year period".
We have then:
y = 1.76 * x
y = 1.76 * (3.09)
y = 5.44 million Americans
Answer:
the number of Americans on probation in 2010 might be:
y = 5.44 million Americans