Chapter 4.1, Problem 60E

Credit Market Debt.

Since 2009, the annual rate of change in the national credit market debt can be modeled by the function

$D^{\prime }\left(t\right)=33.428t+71.143$,

Where $D^{\prime }\left(t\right)$ is in billions of dollars per year and t is the number of years since 2009. (Source: Based on data from federalreserve.gov/release/g19/current.) Use the preceding information for Exercises 59 and 60.

What was the national credit market debt in 2013?