Final answer:
The subject of this question is Mathematics and it discusses a rule about the percentage of income to be spent on housing.
Step-by-step explanation:
The subject of this question is Mathematics. The question is asking about a rule regarding the percentage of income that should be spent on housing. The rule states that it is good to spend no more than 25-30% of your income on housing. This rule helps individuals manage their finances and ensure that they have enough money for other expenses.
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