Average Calculation

Hi Experts,

I have a formula like this:

=IFERROR(VLOOKUP(B4,INDIRECT("'"&$C$2&"'!"&"B28:H77"),2,0),0)+IFERROR(VLOOKUP(B4,INDIRECT("'"&$D$2&"'!"&"B28:H77"),2,0),0)+IFERROR(VLOOKUP(B4,INDIRECT("'"&$E$2&"'!"&"B28:H77"),2,0),0)+IFERROR(VLOOKUP(B4,INDIRECT("'"&$F$2&"'!"&"B28:H77"),2,0),0)

Output

=10+20+0+30

more than Zero value =3

Here I want the formula to calculate the average by which gives the value more than 0
i.e 60/3=20 IF four no found more than zero 60/4

Thanks in advance..!