#### Answer

b. $100~cm^2$

#### Work Step by Step

If a dollar bill is 5 cm long and 2 cm wide, then it would have an area of $10~cm^2$. Clearly, these dimensions are too small for a dollar bill.
If a dollar bill is 15 cm long and 6 cm wide, then it would have an area of $90~cm^2$. These dimensions seem reasonable for a dollar bill so an estimate of $100~cm^2$ is a good estimate.
If a dollar bill is 40 cm long and 25 cm wide, then it would have an area of $1000~cm^2$. Clearly, these dimensions are too large for a dollar bill, so an estimate of $1000~cm^2$ is too large.
Clearly $1~m^2$ is much too large for the area of a dollar bill, since a square with sides of 1 meter has an area of $1~m^2$.
The area of a dollar bill is approximately $100~cm^2$.