Help with division

I may not even be calling it the right thing. but let me explain what i'm looking to do. i've got three columns on a spreadsheet and i need to be able to add two columns together and then divide the sum by another column. so something like this:

4+4/636 = 79.5

d2+f2 (divided by) h2 = 79.5

i'm sure this is going to be incredibly easy for someone and i thank you in advance.