.
sqrt(1575) =~ 40.
Answer. 35 and 45. The number of seats is 45.
If you want more accurate math solution, here it is.
Let the unknown x be the number of rows PLUS 5.
Then the number of seats is (x-5).
According to the condition,
(x+5)*(x-5) = 1575,
x^2 - 25 = 1575 ---> x^2 = 1575 + 25 = 1600 ---> x = 40.
Then you get the answer.
In this way you get the solution of the problem mentally, without using the quadratic formula.
See the lesson
- HOW TO solve the problem on quadratic equation mentally and avoid boring calculations
in this site.
Also, you have this free of charge online textbook in ALGEBRA-I in this site
- ALGEBRA-I - YOUR ONLINE TEXTBOOK.
The referred lesson is the part of this online textbook under the topic "Quadratic equations".