It always helps to draw it out if you are in doubt.

So sketch the function and draw the corresponding trapeziums.

I assume by , you mean that you want 2 subdivisions.

Since the horizontal distance is units, then each subdivision will have horizontal distance of unit.

This is the same as the height of the trapezium.

Now for the parallel sides of the trapezium, you will need to evaluate and .

Can you go from here?