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 theleft 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?