Fill average to right for multiple columns

[JODomingos]

Hi Friends.
I need a macro to fill the average formula in the cell B15. The range used, it must be the one selected from above (B2:B12). After that fill the formula right to the next columns (C, D, E......) until the last.
But the point is that the range can be variable, sometimes i have from B2:B67 for instance, so it would be nice if i can use the column A as reference for average until the last row. Because sometimes i have some blanks in the columns. (Pink cells).

Can you help me guys?

Thanks in advance

 

[Dossfm0q]

Book1
	B	C	D
2	-1	-1	-1
3	-1	-1	-1
4		-1	-1
5	1	-1	-1
6	-1	-1	-1
7		-1
8	-1	-1	-1
9		-1	-1
10	1	-1	-1
11	1	-1	-1
12		-1	-1
13
14
15	-0.142857143	-1	-1
Sheet1

Cell Formulas
Range	Formula
B15:D15	B15	=IF(COUNTA(B$1:B$11)<>0,SUM(B$1:B$11)/COUNTA(B$1:B$11),"")