So you are calculating , meaning you have to divide the interval into six equal portions. And to find how long each of the sub-interval is going to be, you will have to use this formula:
For dividing into n sub-intervals.
So, you should have as the length of your subs.
Now, you need to use the formula:
Note that and , so in this case is equal to , because we are using the left end points
So once you have plugged in all the value, you should have the following expression:
Using , just plug in the values! Can you take it from here?