i have this question, i dont want to type it all out, because its long but i have a picture of it
The area $\displaystyle A$ under the function $\displaystyle f$ on the interval:
$\displaystyle a\leq x \leq b$
is given by the formula:
$\displaystyle A=\lim_{n->\infty}\Sigma_{i=1}^nf(x_i)\Delta x$
$\displaystyle x_i=a+i\Delta x$
$\displaystyle \Delta x=\frac{b-a}{n}$
Try using that formulation of area. It provides a little more information which should be helpful. It's basically the same formulation on your problem sheet, but I provided more information about $\displaystyle \Delta x$.
Let me know if this helps. If not, I'll add more.