Visual Algebra

One circle is added to the height on each step. The heights of the first three steps are $4,5,6.$ So, the height of the next step is $7.$

How many circles are in the height of step $4?$

At each step, the height is $3$ more than the step number. So the height of step $n$ is $n+3.$

How many circles are in the height of step $n?$

At step $n,$ the base has $n$ circles and the height has $n+3$ circles. To get the total circles, we need to multiply base and height, which gives $n \times (n+3).$