The next interval goes from 20 to 24. The next interval goes from 24 to 40. And if the whole notion of a Riemann sum is completely foreign to you, I encourage you to watch the videos on Khan Academy on Riemann sums. And so here we are. So the first interval is from zero to 12. And so we want to use the value of our function on the right side to define the height of the rectangle. So let me define.