Hello. Very interesting project!
The formula contains 4 pieces of information:
1. Diameter of the sun. This is what you are measuring.
2. Distance from the earth to the sun. You are not given this. You will have to research to find this.
3. Diameter of image of sun. You measured this.
4. Distance from pinhole to the image. You measured this.
After researching and finding the distance from the earth to the sun, the next step will be to rearrange the formula to solve for diameter of the sun. If you don't know how to do this, look here to read further:
http://www.themathpage.com/alg/equations-fractions.htm
http://www.purplemath.com/modules/solvrtnl.htm
One final note. All of your distances must be in the same measurement unit! Your measurement results are in cm, but distance to the sun will probably be given in miles, and you will report diameter of the sun in miles. Therefore, you will need to convert your measurements to miles before plugging all numbers into the forumla. If it isn't in your math or science book, there are several online websites to help you convert cm to miles.
Good luck! Please write back if you have any further questions!
