Formula using average

I am trying to plug in a formula to a block

using average.  Here is my discription:

I need to add only the numbers in column G (Lets say G4-G60 if the cell ='s

3 in D4-D60).

Skill Level             Total Experience

3                             6

3                             4

5                            12

7                            36 

7                            24

5                            16

3                             4

I am looking to count only the "Total Experience" that is listed as a skill

level of 3 (5 or 7 for that matter as well) and average the total to the

number of skill level listed.

Formula's anyone?