The Sahara Desert covers about 8.3x10^13 sqaure feet.

The average depth of the sand in the Sahara Desert is 200 feet.

A grain of sand has a volume of approx. 1.3 x 10^-9 cubic feet.

Which of the following is the best estimate of the number of grains of sand in the Sahara Desert?

A. 10^22

B. 10^23

C. 10^24

D. 10^25

Can anyone let me know how to go about solving this problem? I know these are in scientific notation, but I have no idea how they get to these answers.

Does anyone know the answer?