Funding for Afghan Security. The number of U.S. forces in Afghanistan decreased to approxi...

Funding for Afghan Security. The number of U.S. forces in Afghanistan decreased to approximately 34,000 in 2014 from a high of about 100,000 in 2010. The amount of U.S. funding for Afghan security forces also decreased during this period. The function

f(x) = −1.321x2 + 5.156x + 5.517

can be used to estimate the amount of U.S. funding for Afghan security forces, in billions of dollars, x years after 2009 (Source: U.S. Department of Defense; Brookings Institution; International Security Assistance Force; ESRI). Use this function for Exercises.

In what year was the amount of U.S. funding for Afghan security forces about $10.5 billion?