#Incorrect argument due to #Divide by zero

I have been attempting to create a formula where I will not have to manually update this every month. My "OSHA Loss Time Rate" is broke down by month (Jan-Dec rows), the 7.78 formula is "=(([Lost Time Cases]@row * 200000) / [Hours Worked]@row)", however if I do not have any hours in or a 0, it shows the #DIVIDE BY ZERO, due to nothing there. I have seen numerous posts talking about the IFERROR formula, however I have no idea how to use it. Since I have the hours in for January (first line with 7.78) but none for February, I am assuming I need to add the IFERROR option included in the formula for the OSHA Loss Time Rate? If so, how would you do that formula?

The other issue is that the top grey #INCORRECT ARGUMENT is due to needing to get the average of all the months (Jan-Dec) below that line. Once again, I am assuming I need to add in the IFERROR formula due it trying to calculate the average but there is an error (#DBZ).