1. you need to add an average at the end of column F, that averages those values. cell F9 in the example of your document
2. open solver.
3. in the set objective box, type whatever cell you have your average in, in the case of your document type $F$9
4. check the circle for "value of" and in the box to the right of the circle type 0.78
5. in the by changing variable cells box type $B$4:$B$8
6. click the "add" button next to constraints
7. in the cell reference box type $F$4:$F$8
8. make sure middle box has = sign
9. under constraint box type 0.78
10. click add
11. leave everything else as is
12. press solve and you will see the cell values change before your very eyes.
13. Most Important --- Don't forget to rate this question 3 stars or better so I am paid for my time.