What you're being asked to do is to look at this Riemann sum & look for patterns.
It says to use A = 0 so we have some information already, you'll see how helpful that is in a second.
What we know so far:
Okay, what is the definition of a Riemann sum?
I could do the rest but I'll let you read this and see if you can figure the rest out on your own, if not I'll help you some more