Here's how a regular dodecahedron looks:
 
All 12 faces of a regular dodecahedron are 
congruent regular pentagons:  



The area of a regular pentagon is given by the formula



[If you don't know this formula, then ask me how to get it
in the thank-you note form below and I'll get back to you
by email.]

All 12 faces of the regular dodecahedron together have area 12
times that or



Thus in this case,



 



Rationalizing the denominator gives:



Edwin