Question regarding Leviticus Chapter 5

Hey, it's Bible study time! I am reading my Bible while the BOYS are in the basement having male bonding time. I am reading in chapter 6 of Leviticus, where the Lord is spelling out what the acceptable sacrifices would be for a sin offering. Verse 6 says

And he shall bring his trespass offering unto the Lord for his sin which he hath sinned, A FEMALE FROM THE FLOCK, A LAMB, OR A KID OF THE GOATS, for a sin offering

(yes, the capital letters are mine for emphasis)

Verse 7 says

And if he be not able to bring a lamb, then he shall bring for his trespass which he hath committed TWO TURTLEDOVES, OR TWO YOUNG PIDGEONS, unto the Lord

Verse 8

And he shall bring them unto the priest...

Verse 9

And he shall sprinkle of the BLOOD of the sin offering upon the side of the altar, and the rest of the BLOOD shall be wrung out at the bottom of the altar; it is a SIN OFFERING

Then suddenly, in Verse 11, there is this VERY confusing contradiction...

But if he be not able to bring two turtledoves or two young pidgeons, then he that sinned shall bring for his offering THE TENTH PART OF AN EPHAH OF FINE FLOUR for a sin offering.

Now, I have a lot of questions about that! How can this be? God requires a blood sacrifice to cover sin. He established that principle in the VERY BEGINNING in Genesis 3:21 when he killed animals to make coats of skins to clothe Adam and Eve in the garden. He went on in Leviticus 17:11 to say

For the life of the flesh is in the blood: and I have given it to you upon the altar to make an atonement for your souls: for it is the BLOOD that maketh an atonement for the soul.

And again in the book of Hebrews 9:22 the writer says clearly

And almost all things are by the law purged with blood: and WITHOUT SHEDDING OF BLOOD IS NO REMISSION (of sin).

And obviously... Jesus Christ made the ultimate sacrifice for sin by shedding His own blood to cover our sin.

So, how does God say a sin offering should be a lamb, a kid of the goats, two turtledoves or two pidgeons, and then contradict it all by saying OR... if you don't have that, then bring a tenth of an ephah of fine flour?? This is not a blood sacrifice offering!?!? If this is the case, then WHY was Cain's offering not accepted in Genesis 4:3-5? If a tenth of an ephah of flour is acceptable in lieu of a blood sacrifce, then why is Cain's offering of the fruit of the ground not acceptable? I am sure there is an answer... I just don't know it yet. This is going to require some thought, prayer, and study. Any ideas from you all in the gallery? I'd love to hear your thoughts! Thanks!