7.4. Natasha and Inna bought the same box of tea bags. It is known that one tea bag is enough for two or three cups of tea. Natasha's box was enough for only 41 cups of tea, while Inna's was enough for 58 cups. How many tea bags were in the box?
Answer: 20.

Solution: Let there be $n$ tea bags in the box. Then the number of brewings can vary from $2n$ to $3n$. Therefore, 58 is not greater than $3n$, which means $19<n$. Additionally, 41 is not less than $2n$, so $n<21$. Since the number of tea bags must be a natural number that is less than 21 but greater than 19, there are exactly 20 tea bags in the box.

Criteria: answer only - 0 points, answer with verification - 1 point. Correct system of inequalities without conclusions - 2 points, correct system of inequalities and correct answer - 4 points. Proof of one of the estimates for the number of packets in the pack (that there are not fewer than 20 or not more than 20) - 3 points regardless of whether the correct answer is given. These points DO NOT add up.