Does the phrase how much more mean to add or subtract?

Answer 1

It depends on the context. For instance if I ask, "I have 3 apples, how many more will it take to make 7?" the best way to get to the answer would be to subtract what you already have (3) from the target amount (7). Or you could add one at a time until you get 7. Either way, you get 4 as the answer.

Normally, this would imply adding, but if you already have the answer and need to find the other value to get there, then you must subtract.