I'm not sure how to use Riemann sums with summary notation..please help?

The function y = f(x) is graphed below:

http://imagizer.imageshack.us/v2/800x600q90/841/a45g.jpg

Which of the following Riemann sums yields the exact area under the curve on the interval [0, 6]?

I. R=E(above=4)below=k=1 f(wk)deltaxk, where subdivisions are at {0, 2, 3, 4, 6} and right-hand endpoints are used.

II. R=E(above=4)below=k=1 f(wk)deltaxk, where subdivisions are at {0, 2, 3, 4, 6} and midpoints are used.

III.R=E(above=6)below=k=1 f(wk)deltaxk , where 6 equal subdivisions and right-hand endpoints are used.

I only

II only

III only

I and II only---my answer

I, II, and III