When doing physics problems, I would advise that you always include units and description in a comment off to the side to make sure it is easy to spot mismatches. E.g.,
Just looking at it, the A term, which I assume is Area, is very suspicious with that R^4 term giving what looks like m^4 for the units. I would expect this to be m^2 for the units. So maybe this should be an R^2 in your formula (only you know the shape of your object and what the correct formula for the cross-section area of your object is ... but the units must come out at m^2 to be valid for the downstream code). If it's a sphere then maybe you just need pi*R^2 on the rhs.