Is this a question off the television , if so there has been quite a bit of a debate on these programmes . They don't tell you how the answer is arrived at and it is a premium rate number you have to call . Only one winner as far as anyone can see.If not , then sorry , no idea how they get that answer .
I've just thought that for the first digit of the answer
ninety + 24 could be
9+0+2+4 = 15 = 1+5 = 6
It should be pretty clear from this that there are hundreds of possible answers to this question, but only one is acceptable, so your chances of winning are slim to say the least.