I wish they would stop using "take away." It's only used by small children learning subtraction for the first time.
We use 'take away' because the Welsh word used for subtraction is 'tynnu' which is 'to pull' or literally 'take away', and which is a word used in many other contexts apart from Maths.
Elsewhere the numeric equivalent, i.e. in this case 9 - 4, is accepted, but not here? Why is that?
Because it hadn't been added yet, each answer has to be entered manually and I'm sure you can imagine that is a very arduous task. In some ways we have been too accomodating in adding every possible combination which means we have occasionally missed one.
Thanks for pointing this out, that'll be fixed now.