Please help me with this. I've seen two online lectures, attended my class lecture, read what the book says, even checked WolframWorld, to no avail.

"use left and right endpoints and the given

number of rectangles to find two approximations of the area of

the region between the graph of the function and the x -axis

over the given interval"

I can't use anti-derivatives yet. The formula we got is:

A = The limit as x approaches infinity of: The sum of the product of: f(x_{i}) * 'delta x', with n = number of rectangles, and i = 1

I really don't get this problem:

f (x) = 9 - x

The region is [2,4]

the number of rectangles, n = 6

This is my latest attempt, can anybody tell me what I'm doing wrong???

{See below for screenshot of my attempts please}

I only have today and tomorrow morning to figure this out, does anybody have resources where I can look up how to do this? I've read a lot of stuff but I just can't get it.