Hi! :)
This question states that four families each brought the same number of chairs. We know that 27 chairs are needed overall and 3 are still needed after the four families' contributions.
Knowing this, you can figure out that you could do 27-3. This equals 24, so you would then just divide 24 by 4, since there are 4 families.
Your final answer should be that each family brought 6 chairs.
Hope this helps!