Find a lower estimate and an upper estimate

*a* = 20

http://www.webassign.net/scalcet/5-1-001alt.gif

(a) By reading values from the given graph of *f*, use five rectangles to find a lower estimate and an upper estimate for the area under the given graph of *f* from *x* = 0 to *x* = 40.

*A* http://www.webassign.net/images/apx.gif (lower estimate)

*A* http://www.webassign.net/images/apx.gif (upper estimate)

(b) Find new estimates using ten rectangles in each case.

*A* http://www.webassign.net/images/apx.gif (lower estimate)

*A* http://www.webassign.net/images/apx.gif (upper estimate)

for (a) i got the width (40-0)/5 which is 8...but it says estimate using 5 rectangles...how would i get the area of 5 rectangles if the width is 8....

same problem with (b)