Rectangles, not Squares

In a figure like that, where parallel lines intersect each other at right angles to form a grid of squares, if there are $a$ horizontal parallel lines intersecting $b$ vertical parallel lines, then the number of rectangles that can be formed is equal to this. $\binom{a}{2}\times\binom{b}{2}.$ Plugging in $a=b=4,$ the number of rectangles in the figure is equal to this. $\dbinom{4}{2}\times\dbinom{4}{2}=6\times6=36.$

The number of squares that appear in an $n\times n$ grid of squares is equal to this. $\sum_{k=1}^nk^2$ Plugging in $n=3$ yields $1+4+9=14$ squares in the figure.

Finally, the number of rectangles that aren't squares in the figure is equal to $36-14=\boxed{22}$

I didnlt have a formula type approach to this problem. I did this by looking and forming the rectangles. Please explain me the formula that you ( trevor B ) used.