Answer
$9$ seats
Work Step by Step
Let $x$ be the original number of rows and $y$ be the original number of seats in each row.
The system of equations is:
$$\begin{cases}xy=72\\(y+3)(x-2)=72\end{cases}$$
From the first equation:
$$x=\frac{72}{y}$$
Substituting into the second equation:
$$(y+3)\left(\frac{72}{y}-2\right)=72$$
$$(y+3)\left(\frac{-2y+72}{y}\right)=72$$
$$-2y^2+66y+216=72y$$
$$-2y^2-6y+216=0$$
$$y^2+3y-108=0$$
$$(y-9)(y+12)=0$$
$$y-9=0$$
$$y=9$$
$$y+12=0$$
$$y=-12$$
Taking the positive value, the original number of seats of each row is $9$ seats.
