The answer to this maths problem is that three people speak both French and Spanish.
Explanation: How To Arrive At The Solution
Out of the 15 people, the 3 who do not speak either language are not relevant to the question, and so we can start by removing them from the equation completely. 15 - 3 = 12, so we are left with 12 people. The 7 French speakers and 8 Spanish speakers must come from this group of 12 people.
7 speak French and 8 speak Spanish, but 7 + 8 = 15, which is more than the total number of people who speak either language. We only have 12 language-speakers, so the Spanish and French groups must overlap, with some people being able to speak both languages.
15 - 12 = 3, so the French and Spanish groups overlap by 3 people.
This means that 3 people must speak both French and Spanish.