Area in square inches of the Earth's Surface
The area of the Earth in square miles is 197 million.
There are (12 x 5280)2 square inches in one square mile.
This equals 12 x 12 x 5280 x 5280 or 4.01 billion square inches.
Multipy the two - 1.97 x 108 x 4.01 x 109 = 7.9 x 1017 square inches on the entire surface of the Earth.
The surface of area of habitable land is significantly less. There are clearly no more than 49 million square miles of such land.
This amounts to 4.9 x 107 x 4.01 x 109 = 1.96 x 1017 square inches.