Focus on the relationship between the output F and the inputs ABCD. In other words: treat the whole thing as a black box with inputs ABCD and output F.
"Excess-3", strictly speaking, operates on BCD (binary coded decimal) values. Since the input is not constrained to BCD, it's better to say "So must I like just add 3 to the input..."
Not making fun, just trying to make a fine point. And yes, then do the comparison.