Answer
$8.8265\times10^{8}$stacks of quarters
Work Step by Step
By dividing the national debt by the value of each stack, the number of stack required to pay it off will be calculated. The value of each stack was calculated in part c to be 18368 dollars.
$16,213,166,914,811 dollars\times\frac{1stack}{18368dollars}=8.8265\times10^{8}$stacks of quarters