selecting and use cells with the same value

Dear sir/madam

You begin by looking to the value of the first cell in column B now you have to look if there are other cells in column B with the same value.

2. if you found cells with the same value you go one cell to the right (so to column C) and you have to look to the value of that cell(s)

3. Now sum up the the numbers of the selected cells of column C and divide them by the number of cells you selected. This value is the answer.

I have attached my excel file

I really tried a lot so I hope that someone can help me!