The figure below shows a graph of line PQ. Determine the equation of line RS which is the perpendicular bisector of line PQ above in the form ax+by=c where a, b and c are integers.

From the graph, point P is at $(-4, -4)$ and point Q is at $(4, 4)$.

The midpoint formula is $M = \left(\frac{x_1+x_2}{2}, \frac{y_1+y_2}{2}\right)$.

So, the midpoint M is $(0, 0)$.

The gradient formula is $m = \frac{y_2-y_1}{x_2-x_1}$.

The gradient of line PQ is 1.

Line RS is the perpendicular bisector of line PQ. If two lines are perpendicular, the product of their gradients is $-1$.

The gradient of line RS is $-1$.

Line RS passes through the midpoint M $(0, 0)$ and has a gradient of $-1$. Using the point-slope form $y - y_1 = m(x - x_1)$:

Rearrange the equation into the form $ax+by=c$:

Here, $a=1$, $b=1$, and $c=0$, which are integers.