I cant seem to get this problem:

Calculate http://webwork.math.uwyo.edu/webwork...47d3498f61.png for http://webwork.math.uwyo.edu/webwork...d946c29ea1.png over http://webwork.math.uwyo.edu/webwork...9e55fb8c71.png.

for my delta x I got 3pi/16, then I tried to get my height points which I got to be (3pi/4, 15pi/16, 9pi/8, 21pi/ 16). Then I plugged each point into f(x) added them together and then multiplied by delta x. But its still not right can someone help me figure out what Im doing wrong?

Thanks!