Examine the Riemann sum at right for the area under $f$.

1. How many rectangles were used?

   Hint (a):

   Notice that the index starts at $0$ and ends at $11$.

2. If the area being approximated is over the interval $a\le x\le b$, what are the values of $a$ and $b$?

   Hint (b):

   General form of a left endpoint Riemann sum:$\displaystyle \sum_{i=0}^{n-1}\Delta xf(a+\Delta xi)$

   $a = 3$ is easy to spot in the Riemann sum. Now determine the end value, $b$.

   More Help (b):

   Notice that $\Delta x= \frac{6-3}{12}=\frac{1}{4}$, so each rectangle has a width of $\frac{1}{4}$.

   You already computed how many rectangles there are part (a).