Maths question: 2 oranges, 3 bananas and 4 apples cost £15, how much...?

Working through some sample questions for an aptitude test on a company's website, and there's one type of question that I just can't figure out. Can anyone explain precisely how to go about calculating this? I've tried substituting, but, well... It's been a long time since I've done much... show more Working through some sample questions for an aptitude test on a company's website, and there's one type of question that I just can't figure out. Can anyone explain precisely how to go about calculating this? I've tried substituting, but, well... It's been a long time since I've done much maths like that!

Thanks for any help!

2 oranges, 3 bananas and 4 apples cost £15.
3 oranges 2 bananas and 1 apple cost £10.
How much do 3 oranges, 3 bananas and 3 apples cost?
Update: Oh no! Would just like to edit to say that these are just SAMPLE questions for the actual aptitude test that would be given if I got an interview. I haven't even applied yet, don't see the point if I can't do these silly questions!
Update 2: All equations are there. Perhaps the final equation is that 3o + 3b + 3a = x..?
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