The correct answer is: "by boosting aggregate demand and, in turn, economic growth".
The American Recovery and Reinvestment Act (ARRA) was approved by the US Congress in 2009, during the presidency of Barack Obama, in response to the Great Recession.
It was a package of measures inspired in Keynesian economics, which directed an important amount of money, using public spending a as fiscal stimulus that would boost consumption and investment and, in consequence, aggregate demand figures and economic growth.
The fiscal policy was effective and the US was able to overcome the recession much more quickly than other countries that used other types of strategies such as austherity measures to enhance growth.