Okay, Do you know how to find the surface area?
To solve this we are going to use the free distance fallen formula:

where

is the distance

is the gravity of Earth


is the time in seconds
We know from our problem that the
penny fell off the top of the building and hit the sidewalk below 3.1 seconds later, so

. Lets replace the value in our formula:



meters
We can conclude that the penny fell a distance of 47.098 meters
The answer would be 6.3, Three squared is nine and the missing side needs to equal 49. 6.3 squares and 3 squared will equal 49.
The answer is 7 7/8. Hope this helps!
Here's the math: